There is no reason not to use Syncthing besides KDEConnect has features other than sharing files that might come in handy.

Syncthing is a much better tool for a hands-off approach once set up so sure, why not?

The Windows version used to be shit. That’s no longer a problem. That’s about the only negative I remember. Otherwise you can have it doing a lot of work between devices or only sending when you feel like it. I force stop it on my phone and then invoke through share when needed.

I brought up Syncthing as it will function the same way, in a more hands off way (by choice if you want, automagically or forced) if you needed to share files/folders between devices. Not only for passwords.

Local file sharing:

I use KDEConnect on all my devices (Windows, Linux, GrapheneOS, Work Galaxy Tab) and it works just fine. Never needed to try anything else.

Syncthing as well for keepass files.