Yup. That’s my one hangup. Except you don’t even need to install Dropbox. It just uses the Dropbox API (correct me if I’m wrong please).
The developer is a single(?) person based out of Germany and is pretty chill. I didn’t know it had Ubuntu and all support till after using it for a long time. I literally would use it just for iOS to Mac and back.
I agree with others that you need to break down these requirements into multiple apps. I use FreshRSS for feeds and it has a bunch of mobile app integrations.
And the most recent update of Linkwarden seems to have a ton of features that might be worth your while, including PDF, screenshot, and Readable caching.
https://linuxiac.com/linkwarden-2-8-bookmark-manager/