Full screen mode no longer possible after game crash

Hi there, I was sent here by Minecraft Support because I cannot get rid of a special problem:

I started Minecraft and played for a few minutes when the game crashed and I was put back in the launcher. (Exit Code 0). 
After I started the game again, I couldn't play it "smoothly" anymore.
I try to update the Java version, restart the computer and uninstall Minecraft myself (including deleting the entire .minecraft folder) and reinstalling it from the official minecraft.net page were unsuccessful.
I don't have MCLeaks or similar third party software installed on my computer. I have a relatively good computer and I play Minecraft with 30 Chucks sight with all other graphics settings at maximum. Then have
I usually 50-70 FPS. Now I'm playing at 9-12 FPS !!
Only in window mode can I increase my FPS to 20-25, but NOT with reduced graphics settings, even if I set everything to a minimum I can't get an increase in FPS, nothing changes! I have attached two screenshots to you: once in full screen mode, once in window mode with all the data.