Read specific raster files and create a mean raster in R

I am desesperate, because my problem seems very simple, but I cannot find out how to manage it.

-> Aim: 1) I would like to read 1 to 4 raster files from a folder. The names of the one that I need are listed in a list as character. 2) After having opened the files, I would like to create a new raster corresponding to the mean of the files.

I can manage it on QGIS, but I need to automatize hte process, as I have a lot of individuals!

1) It should work with list.files(pattern = ) but as the names are in a list, I do not know how to do. Ex: for the first individual, I have to read 2 files named "2018-12-27_sic.tif" and "2018-12-27_sic_con.tif"

I tried to read with readGDAL , open.GDAL it didn't work

thanks a lot for your valuable help