iMac 2019 lagging

Hi guys

I need to ask the community the following:

For 2 days ago woke up to find that my IMac 2019 intel i9 crashed over the night and both of my external screens stoped working!

I basically started then to Google about the issue both new usb-c adapters changed the cables nothing worked.

That was the time when I decided to call Apple and after talking with them for 2 hours the decision was to upgrade to Big Sur. BIG MISTAKE!!

The machine started lagging got lines on my screen and the external screens are still not working.

Then I decided to erase the HDD and reinstall Big Sur. SECOND BIG MISTAKE!!
It got even worse :(

Then I decided to downgrade to the previous Catalina OS from a bootable USB.
The machine is still lagging and the screens still not working. Then I decided to downgrade to Mojave the OS the machine came with, well still same lagging and screens not working :(

Everytime I did the above solutions I did a clean install

Now any of you amazing ppl can have more to add to my solutions?
I got green light from Apple that I can send the machine to one of they’re service place but my problem is that i live really remotes and I will be without a PC for like a month, that is why I am asking you ppl for more brainstorm maybe I can fix the problem without sending the machine to Apple?

iMac 2019 lagging
 
 
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