This is a workaround to a linux mint(muffin) bug here #656
How it works is by intercepting the fullscreen event and forcing the fullscreen to the window your cursor is on
Dependancies
sudo apt install libx11-dev libxrandr-dev
Clone the repo
git clone https://github.com/IrishBruse/mint_fullscreen_fix.git
Move to the folder
cd mint_fullscreen_fix
then build the application
make
to test it out you can run
./mint_fullscreen_fix
If it works to fix it you can the set it to run on startup using the starup application app like below
