Thank you for your reply.
First of all, I did a backup.
Secondly, I tried to update the clover boot loader via the clover configurator but I get an error message that it cannot connect to the stable and beta servers of the app... In any way, I found and downloaded the package of clover r.5018 and I can install it manually.
The problem is that the boxes in r5018 are different than the guide in the 1st post. So I don't really know what exact boxes to tick.
My last problem is the following. I tried to make the update (without updating clover, I just updated the kexts), and I destroyed my system...
I had to wipe the disk and time machine my way back to the desktop.
One problem that I faced was, I think, the GPU rx480. I think that I have to remove it from the motherboard, and them connect the monitor directly to the Display port of the tower (not the DP of the GPU), and use the integrated intel GPU. Otherwise I get to a completely black screen.
Sniki is that correct? Do I have to remove the GPU before proceeding to update?