It uses a database and it's totally possible to use SQLite as the database and sync that elsewhere. You could then find or make a small client that just accesses that db directly rather than a web service, I suppose. Though there are already several apps out there that store passwords locally and their data files can be synced, if that's what you want.

But if you're doing that then you may not be using this in the most common way or may not understand the risk involved. This is likely to have every one of your logins, not just a single login that may or may not be used on other sites, but the specific username and password and which site it's associated with. On addition to access to those accounts, this links all of your accounts to a single identity which companies spend billions to do with advertising IDs, cookies, embedded scripts, and lots of other, usually shady, practices. This is a gold mine, though usually only for one or a few users, so generally not a major target unless you're being targeted personally for some reason. So, even if they don't get the passwords, they've now linked every account you have on every site to your identity.

If you are allowing the database to be relatively easily obtained by syncing it to a central location accessible over the internet, a bad actor who gets it can even take their time brute forcing any encryption that may be present in the database, but if you don't keep encryption keys only on your local device because you want to be able to use it elsewhere, then you probably stored the keys along with the db and they dont even have to bother with that, or if it uses password based encryption, they just have to guess or brute-force a single password.

If it's behind a properly secured web service, then even if they find an exploit in the server software, they likely have to do many queries over time to get much data and the server can mitigate that risk and/or alert the owner about new logins and such. A database in the hands of the bad actor can't complain about too many attempts to access it or notify anyone that it's been copied.

So, IMHO, it's a bad idea to use synced local password managers unless you have a very robustly secure way of storing the database and the encryption keys.