For example I’m not aware of any way to do upload without a login in Seafile.
You can create upload share the same way you create a download share. Then just give a link to whoever you want to and that’s it. I’m pretty sure it’ll show files already in the share while uploading, but I’m not 100% sure on that.
I did self-host bitwarden and it’s not that bad to keep updated and running after initial setup (including backups obviously) but it still requires some time and effort to keep it running. And as I was the only user for the service it just wasn’t worth the time spent for me (YMMV) so I switched to their EU servers and I’ve been a happy user ever since.
What I should do is to improve local backps on that, currently I just export my data every now and then manually to a secured storage, but doing it manually means that there’s often too long time between exports.