Notes Gone After Mac Update to Catalina

Hi! I recently updated my MacBook Air to Catalina and discovered that all my Notes had disappeared. These notes go back six years, and I'm desperate to get them back. I've tried everything - I scoured the Recently Deleted files (found nothing), converting my group.com.apple.notes into .html (it was a wall of gibberish), logging into my iCloud.com (again, nothing). I did manage to go into my Time Machine (since I backed my computer up before the update), but for some reason, I could only recover a few notes out of the hundreds that I've lost.

I found all my notes in my gmail 'Notes' folder, and I definitely remember ticking the 'sync' option in my iCloud before the update, but now I can't seem to access them or find them in a form other than email. Is there any way to move my gmail 'Notes' folder into my actual app, or recover my old notes somehow? Some of these notes mean a lot to me, and I would appreciate any advice in getting them back. Thank you so much!