I have downloaded the patch files manually. always did.
Originally my game was 1.03 (havent played in a long time). the patch from 1.01 to 1.10 gave me errors so I thought maybe it's because of the 1.03 version.So here is what i did:

1. redownloaded the game manually, installed it succesfully and it runs at version 1.10.
2. downloaded the 1.21 patch.
3. haven't attempted to install dlc.

I get these errors in order:

I had look on the net for that error, people suggest a virus/malware scan. or it could be bad ram :(

The game runs fine, and there is no malware on my computer. Other similar demanding games, like DOOM 2016 run fine. I also have succesfully patched witcher to 1.01 to 1.03 in the past.

I downloaded GOG galaxy and that way it updated to 1.21 just fine.