It's an issue with the inventory expansion that they did. Expanding player inventory through regional banks and the mount inventory system. It needs some heavy optimization. If they can't get it optimized by EA I wouldn't be surprised if they removed mounts until they can get it figured out, which would be unfortunate.
.deb appimage worked out of the box for me on Ubuntu for launcher at least. Used their recommended config from there. Here is the wiki and I'll spoiler a discord link to a post I used to get umu to work properly. Only real issue I had was a file repair from patcher was needed because I couldn't see character or load game at initial install.
