I know not an ideal solution but after trying lots of foss applications, we decided to make our own solution. Other than that Nextcloud Deck is more than enough for most use cases

Yes. Nothing wrong with nextcloud. It’s a skill issue

I develop on emacs with same PC config, run sql servers locally, maintain servers, office and mail stuff, all kind of communications, file operations, casting screen to a TV or projector, very good stylus and note taking abilities on my samsung tab 9 ultra dex mode with 4 days of battery life. You may think as an alternative

Windows lol

Is it compatible with android phones?

Yes please go with details

None of them are available in my country