Boost4Lemmy already put a placeholder into Google Play store so people can get notified when a first build drops.

Doing the same with Sync4Lemmy would be a good idea...

Yes, there is. Look at my analysis of costs: https://github.com/mihakralj/obsidian-cloudsync/blob/main/doc%2Fcost.md

Plugin now works on mobile as well. 👍

This plugin works inside obsidian. There are SDK calls to Azure, AWS and GCP using their js libraries and plugin compares local files with files in cloud storage and synchronizes as needed.

Currently there are several node.js calls that plugin needs to work - and node is not available in Obsidian on mobile. Refactoring into pure browser mode app is doable and that would make it work on mobile.