Flask patterns for web dev

I am new to Flask and Python, and I did my best to develop application in line with patterns presented in official documentation.

Link : https://flask.palletsprojects.com/en/1.1.x/patterns/

I went through number of videos on YT and webpages.

Finally I ended up with project on GitHub, but still I am not entirely sure if I took the right path, so how this code should look like ?

GitHub : https://github.com/DrStone92/FlaskTemplate

Issue1 : I cannot insert values to database. I think database is not initialized in right place.

Issue2 : I tried few methods of passing values across blueprints, finally Session came in handy. I saw some examples with g but I couldn't understand how someone did it. Idea is to get rid of passing number of parameters into templates.

If someone could point where I made mistakes in the code, review and guide me a bit, I would be grateful.