Dell XPS 15 9560 Ubuntu Slow boot / WIFI problems

I have problems with my Dell XPS 15 9560 Ubuntu 20.04.

First, the WIFI started to have connection problems. Then reboot started to get slow (minutes instead of seconds). Also when you wanted to log in it took a minute before you could input any text. After that, it was nice and fast.

A few reboots later the WIFI didn't do anything anymore. The laptop was extremely slow. I checked the temps and the CPU was heat throttling.

So I opened the laptop and started cleaning the fans(they were really dirty). Also noticed I got the famous killer wifi switch. After cleaning I booted up again. Still slow boot and no Wifi. I did the DELL Diagnostic (boot option) and it couldn't find any problems. Fans were spinning normally.

So I thought it was the killer wifi adapter. I disabled WIFI in the bios, but still super slow boot. I tried to install an old USB wifi adapter (didn't work). But now after boot, the screen gets darker than normal, and I can not adjust it. Also, I checked the SSD and the benchmarks were good.

I don't mind doing a reinstall and installing a new WIFI chip, but the dimmed screen got me worried. Are these the last moments of the laptop(RIP?) Or do you think with a new Ubuntu install and WIFI chip it can work properly again?