How can I sync+backup Windows-Mac-IOS for free?

Things I have tried

I’ve tried iCloud and obsidian git but quit because git broke and iCloud acted funky with Windows, the results didn’t show on Mac after editing on Windows but I could manually redownload the file and it showed, which was stupid.

Syncthing doesn’t work on mobile because I can’t specify the folder I want to use on the obsidian app; I can only use iCloud or make a new vault.

What I’m trying to do

I want to sync Windows-Mac-IOS as fast as possible (WITHOUT paying), as well as have backups/“snapshots” of the folders every time I edit them.

if iclould and git don’t work for you, you can’t.

Yes I agree with WhiteNoise.

set up git. This is what I use to sync between two PCs and an Android phone for free.