Why do I have a lower frame rate in fullscreen?

co
3

I'm using a 2007 iMac. I know it's pretty old, but I'm only using it temporarily.
So my question / my problem is whenever I enlarge the window, my frame rate goes down. Not only in chrome, Discord etc. But also in games like Minecraft
1-2 weeks ago everything went quite normally. I'll take Minecraft as an example. When I have the window very small. I have about 150-200 fps. I make it bigger / in the full screen I have about 5-20. I've already tried everything. Software reinstalled, etc. What I have to say is that I'm new to MacOS. Before that I only used Windows.
So it would be nice if someone could help me as soon as possible how to fix the problem.

Pl

If you have something in the window mdous, the resolution is lower, at least usually. In other words, if you set it to full screen, it is usually set to the highest what your monitor can do. You can't really change anything about it. In the MacOs settings you can also manually lower the resolution.

co

OK? But 1-2 weeks ago everything worked normally without losing fps

Pl

Unfortunately, I can't say more. I'm not a Mac user xD