Flutter

It depends on what your needs are. Database drivers for connecting straight into a database server will be limited. Dart just hasn’t gained as much momentum on the server side as other languages and most apps use an n-tier architecture so no need for drivers. There’s no server side rendering for flutter so your app startup time might be a hinderance for a user just wanting to pull up a web page and see some data.

Small desktop apps are absolutely fine in Flutter. For your use case I can't imagine there being much problem, beyond connecting to the databases youre using to pull data. You might have to write the API client yourself if it's not a relatively new database server.

I'd say have a go with it. The basics are similar to TKinter and the UI is a lot nicer by default. You'll also find it super easy to run on desktop and web - quite literally just changing what the target is and it'll work out of the box (until you start relying on platform-specific features or packages).

Currently developing a small-ish application with ambitious demands on design with Flutter for all desktop platforms and the web.

I'm only a few months in, but so far it’s going very well. Performance is ok, even on the web (much better on native, of course).

My main advise is to develop on native, because it’s a much better experience, but regularly test on web as well, because the Dart compiler for the web behaves very differently than the native one. There were quite a few surprises waiting for me when I tested it after a few weeks of native development.

For database access you're going to need a web service that provides the necessary access, since Web doesn’t allow for anything more direct. You can use that one for native as well, to keep the code uniform across platforms. I don’t recommend writing that service in Dart, there are much more suitable languages available for that.