Mac mini performance loss?

My problem is this. I have a Mac mini (late 2012) and everything worked great but since the last update to MacOS 10.15.7 it hangs on all corners and edges. When I'm looking for something in Safari it takes forever, games that previously worked just hang (for example Minecraft) and it takes forever to start something. Now I ask myself whether it is the Mac itself, or if it is the system, how can I downgrade the system?

That is probably because of the new MacOS you have installed, but look at it this way: You are using very, very very outdated hardware and with every year you continue to use it, it gets older, the software more demanding and at some point you just don't come anymore With.

When did you install the update? Just or was it a few days ago?

Immediately after the update, all databases and indices are recreated internally and the computer can react more slowly for a day. This should improve after two days of use at the latest.

If you're using FileVault on an HD, it can also take a few days longer for everything to be encrypted and back to normal.

Did the update about 2 weeks ago

If the hardware such as the processor, graphics unit, etc. Is already out of date then the new type of software does not keep pace, because the hardware is working at full speed and is at full capacity so that the software somehow works at all and whether the PC is hanging on all the time. In order for (new) software to work properly, you need the appropriate hardware that is designed for it. But this is the case with all PCs, Windows 10 would not work properly on a 20 year old computer either, or the latest Mac OS would not work on the 1st generation Mac either.

Thanks for your help. Could you tell me how I can get back to an older MacOS version?

If your Mac ran for a long time in the two weeks, everything should be done. Only FileVault may take longer. Did you activate that?

Otherwise, take a look at the activity display to see if any programs or processes are using a lot of CPU power.

So it is an average of 50% GPU utilization inactive, 5 of the 8GB RAM are occupied and I can't get it down

The question is not what is inactive, but what is causing the remaining 50% CPU usage. Do you notice anything?

Some windows server he says

Not at all in the normal or legal way! This is only possible with certain programs, but whether they are trustworthy or safe is also very doubtful. At this point I can really help you but I would not. It's best to see a computer specialist, or you have to get a new computer for better or worse.