Do you block third-party cookies? It prevents Drive downloads in any browser with that setting, Chrom{e,ium} included. Recently I saw Drive give a suggestion about this, but a year ago when I was testing third-party cookie blocking in Chromium it took me a day or two before I figured out the connection.

"even changing my user-agent to Chrome, and it works flawlessly." implies that blocking third-party cookies is not the culprit.

I experience the same. Can't really use YouTube, can't download files from gdrive. Google was the best thing that could happen to search engines. Chrome was a godsend. Now they are what Microsoft was two decades ago (Microsoft is still full of shit, but now they are not alone).

What self-hosted option did you pick just out of curiosity? Looking to do the same thing.

As another commenter mentioned, TrueNAS is my go-to for general storage and phone/PC/Mac backups; it's dead simple to setup and is extremely capable, not to mention it'll run on just about anything (barring the ZFS cache RAM requirements...). Personally, I keep a 'master' home folder on there that gets auto-mounted in whatever OS I boot into; this way I never have to go hunting around the NAS for files, for instance I just have a single "Documents" folder that effectively 'syncs' across my Mac, *nix, and Windows. I use CX File Explorer on Android to access the NAS, add a WireGuard VPN (which there's a great plugin for on TrueNAS) and you've got access to your files anywhere.

GDrive I was able to replace more or less with LibreOffice and Collabora, I rarely need to share documents outside PDF or print, which makes compatibility a non-issue for me (and even when I need to, saving as a .doc usually maintains layouts, fonts, etc.).

Nextcloud is pretty great. I use it for file storage/sharing, contacts, calendar, and notes. There is a way to run a GDocs clone on it as well but I have no need for an office suite.

FreeNAS is solid.