Sharing this here, to help others that may be having the same issue as I had. Unity Hub got my login info authorization from the browser and immediately logged me into Unity Hub. I clicked 'Remember My Decision' and clicked Yes/Okay. I went back, closed, reopened, and then re-signed into Unity Hub 3.2 it opened the same page in Firefox, but this time it asked me if I wanted to open the link in Unity Hub. Then, realized that Unity discontinued the official AppImage at the beginning of this year (2022) in favor of Debian and RPM packages and everyone was angry, so I decided to make my own. My OS is an Arch-based distro and wanted to use an AppImage for this. I pointed it at /opt/unityhub/unityhub-bin. AppImages are back So, for a university project I had to use Unity. I used the dropdown to 'choose an application' for the links. I went into Firefox's settings, looked for unityhub in the 'Applications' section of the General settings. That worked, but it still wouldn't sign me in. did a little digging thanks to UnityJuju's comment, and I tried to open ' unityhub://2019.4.8f1/60781d942082' in my browser. When I went to sign into the hub, it opened Firefox and the page that it loaded was a blank page.

Just installed Unity Hub 3.2 removed the old Unity Hub 2.x (AppImage).

Unity hub appimage