Hi, I have a lot of games -if not all- that I cannot play windowed. Only full screen,
Is there a solution for this?

You can try looking here if the game support windowed mode or not. ;)

There is this app named "Gamers Window Relocator" it allows you to play some games in exclusive fullsceen mode. Official site seems to be down. I dunno if you can create windowed mode for games with it if the game got no windowed option.

Also some games like diablo 2 when you add -w at the end of the shotcut's Target field in "Properties" will play the game windowed.

For dosbox games you hold ALT and press ENTER. This should switch between fullscreen and windowed. This may or may not work for other games If the game doesn't have any option for a windowed mode hen it's worth asking about that specific game because their still could be a hidden solution.

I don't know how (or if you can) force all fullscreen games to be Windowed even if they don't have that option..