Obsidian Sync told me I reached the size limit, I have only less than 5 images in my vault, and my largest file is only like 4 MB.
I click purge, somehow it recalculatesthe size, but still occupies like 9.2GB, so it will be filled very soon I imagine.
This happens years ago and I email the customer support, in the end they never find the reason and I need to delete my remote vault and sync again.
I won’t be able to answer your question (as I’m not an Obsidian Sync user 
) but from your 2nd screenshot, I’m not sure your local vault should be located there (i.e.: iCloud Drive > Documents).
I mean, AFAIK, it’s much more than recommended to have the local vault nowhere near iCloud Drive (or any other “cloud services” for that matter).
It’s suggested, in Obsidian documentation, to have the local vault located under:
- macOS:
/users/username/vaults
… Unless this particular screenshot concerns a backup of your vault maybe 
…
If that’s the case, please ignore me 
thanks, will move the folder to suggest space and hope that is the reason why it occupy so much space remotely!
Version history is also part of the remote vault size.
It looks like you deleted a bunch of files locally, or have at least one file that you edit a lot (through some automation)
In your Sync plan attachments are stored for 14 days in the version history, notes for one year.
The only way to remove this before that is to delete the remote vault and create a new one.
(don’t forget to create backups)
