Seperating Unity C# code from "normal" C# code

I had thought about seperating Unity C# code (code that I can only use with using UnityEngine) from "normal" C# code (int x = 3; bool isKnockMeDead = true; void KnockMeDead(); etc.)

Why? So that I could (for example) switch from Unity to Wpf without having to rewrite the whole logic. So my EngineObject is then Window instead of MonoBehviour...

I already have a few solutions to this problem:

But I'm not 100% satisfied with any of them, because...

1st solution - InheritanceSolution.cs

It's the quickest way to do this, but you doesn't have a 100% visual separation and the danger of using Unity Code in the Child class is also given.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using UnityEngine;

namespace Assets
{
    //Unity C#
    public class InheritanceSolutionParent : MonoBehaviour
    {
        public MusicPlayer EngineMusicPlayer { get; private set; }

        public void SetObjectName(string name)
        {
            gameObject.name = name;
        }

        public void MoveObjectUp(decimal y)
        {
            gameObject.transform.position += new Vector3(0, (float)y);
        }
    }

    public class MusicPlayer : MonoBehaviour, IMusicPlayer
    {
    }

    //C#
    public class InheritanceSolutionChild : InheritanceSolutionParent // => Unity
    {
        private IMusicPlayer _universalMusicPlayer;
        private List<Sound> _sounds;

        public void Start() /* => Unity */ => UniversalStart();
        public void Update() /* => Unity */ => UniversalUpdate();

        private void UniversalStart()
        {
            Initionalization();

            _sounds.Add(new Sound("Toilettenspülung", "Assets/Sounds/Toilettenspülung.mp3"));

            _universalMusicPlayer.Play(_sounds[0]);
        }

        private void Initionalization()
        {
            SetObjectName("PartialSolution");
            _universalMusicPlayer = EngineMusicPlayer; // => Unity
            _sounds = new List<Sound>();
        }

        private void UniversalUpdate()
        {
            MoveObjectUp(5);
            MoveObjectUp(2);
        }
    }

    public class Sound
    {
        public Sound(string soundName, string soundFileDataPath)
        {
            SoundName = soundName;
            SoundFileDataPath = soundFileDataPath;
        }

        public string SoundName { get; private set; }
        public string SoundFileDataPath { get; private set; }
    }

    public interface IMusicPlayer
    {
        void Play(Sound sound);
    }
}

2nd solution - PartialSolution.cs

The keyword is actually used if several people want to work on a class without being disturbed and/or if autogenerated code should be separated from the user.

I just use it to separate code, which is ok, but it should not be used to be able to say that every class has 200 lines, because it simply remains one class over when compiling.

And there is the problem :/

Visual separation would be perfect, but nothing changes in the implementation and I can still use Unity code in both(one) Classes.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using UnityEngine;

namespace Assets
{
    //Unity C#
    public partial class PartialSolution : MonoBehaviour 
    {
        [SerializeField] private MusicPlayer _engineMusicPlayer;

        private void Start() => UniversalStart();
        private void Update() => UniversalUpdate();

        private void SetObjectName(string name)
        {
            gameObject.name = name;
        }

        private void SetUniversalMusicPlayer()
        {
            _universalMusicPlayer = _engineMusicPlayer;
        }

        private void MoveObjectUp(decimal y)
        {
            gameObject.transform.position += new Vector3(0, (float)y);
        }
    }

    public class MusicPlayer : MonoBehaviour, IMusicPlayer
    {
    }

    //C#
    public partial class PartialSolution
    {
        private IMusicPlayer _universalMusicPlayer;
        private List<Sound> _sounds;

        private void UniversalStart()
        {
            Initionalization();

            _sounds.Add(new Sound("Toilettenspülung", "Assets/Sounds/Toilettenspülung.mp3"));

            _universalMusicPlayer.Play(_sounds[0]);
        }

        private void Initionalization()
        {
            SetObjectName("PartialSolution");
            SetUniversalMusicPlayer();
            _sounds = new List<Sound>();
        }

        private void UniversalUpdate()
        {
            MoveObjectUp(5);
            MoveObjectUp(2);
        }
    }

    public class Sound
    {
        public Sound(string soundName, string soundFileDataPath)
        {
            SoundName = soundName;
            SoundFileDataPath = soundFileDataPath;
        }

        public string SoundName { get; private set; }
        public string SoundFileDataPath { get; private set; }
    }

    public interface IMusicPlayer
    {
        void Play(Sound sound);
    }
}

3rd solution - InterfaceSolution.cs

(Ey Max please separate the class GameController(big project)...

uh... gotta go run)

The solution is actually perfect, but the effort is quite high!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using UnityEngine;

namespace Assets
{
    //Unity C#
    public class InterfaceSolutionUnity : MonoBehaviour, IInterfaceSolutionUniversalEngine
    {
        IInterfaceSolutionUniversal _universalInstance;

        [SerializeField] private MusicPlayer _musicPlayer;

        public void Start()
        {
            _universalInstance = new InterfaceSolutionUniversal(this, _musicPlayer);
            _universalInstance.UniversalStart();
        }

        public void Update() => _universalInstance.UniversalUpdate();

        public void SetObjectName(string name)
        {
            gameObject.name = name;
        }

        public void MoveObjectUp(decimal y)
        {
            gameObject.transform.position += new Vector3(0, (float)y);
        }
    }

    public class MusicPlayer : MonoBehaviour, IMusicPlayer
    {
    }

    //C#
    public interface IInterfaceSolutionUniversal
    {
        void UniversalStart();
        void UniversalUpdate();
    }

    public class InterfaceSolutionUniversal : IInterfaceSolutionUniversal
    {
        private IInterfaceSolutionUniversalEngine _universalEngineInstance;

        private IMusicPlayer _musicPlayer;
        private List<Sound> _sounds;

        public InterfaceSolutionUniversal(IInterfaceSolutionUniversalEngine universalEngineInstance, IMusicPlayer musicPlayer)
        {
            _universalEngineInstance = universalEngineInstance;
            _musicPlayer = musicPlayer;
            _sounds = new List<Sound>();
        }

        public void UniversalStart()
        {
            _universalEngineInstance.SetObjectName("PartialSolution");

            _sounds.Add(new Sound("Toilettenspülung", "Assets/Sounds/Toilettenspülung.mp3"));

            _musicPlayer.Play(_sounds[0]);
        }

        public void UniversalUpdate()
        {
            _universalEngineInstance.MoveObjectUp(5);
            _universalEngineInstance.MoveObjectUp(2);
        }
    }

    public interface IInterfaceSolutionUniversalEngine
    {
        void MoveObjectUp(decimal y);
        void SetObjectName(string name);
    }

    public class Sound
    {
        public Sound(string soundName, string soundFileDataPath)
        {
            SoundName = soundName;
            SoundFileDataPath = soundFileDataPath;
        }

        public string SoundName { get; private set; }
        public string SoundFileDataPath { get; private set; }
    }

    public interface IMusicPlayer
    {
        void Play(Sound sound);
    }
}

My questions:

1. Is it even necessary? If yes, when?

2. Which of the three would be the best in your opinion?

3. Is there a better one?

In summary, I just want to be a bit more independent from Unity, but I don't want to program a new engine right away.

You can leave up to me how I should design it in the end. (MVVM, MVC, etc.) :)

I look forward to your answers. Please be my heroes!