Ubuntu ships a Chromium browser that has its abilitiy to store passwords safely sandboxed/containerized away.
I did not expect that, given that Ubuntu comes with a full GUI and thus safe password storage backend available in theory.
Because this issue is open since 2022, I wrote a repro that proves its existence:
https://bugs.launchpad.net/ubuntu/+source/chromium-browser/+...
All credit goes to user "Erlenmayr" who reported this.