Only the frontend. Not the backend, so you can’t self host without modifying both browser extension and mobile app, along with rewriting a server from scratch.
The frontend for keypassxc isn’t necessarily horrible, it’s just proton pass feels like magic, while key pass feels just barely working. idk I remember it being kinda awkward
Idk it was so bad it was annoying me, when I tried. Maybe I should force myself to use for a month, and see the results.