Hi sure.

Brave Version 1.46.144 Chromium: 108.0.5359.128 (Official Build) 

Opera GX Your version isLVL 4 (core: 93.0.4585.84)

Version 22.0.8 on each browser

Did more tests this morning and here are some results. Thank god for the backup feature. 

Starting with 119 bookmarks

1. Restored Opera GX to origial state. 

2. Upload to server (Overwrite server data) 

3. Delete all bookmarks from Brave 

4. Merge local and server data on Brave

5. Click Start Synchronization on Brave
6. Click Start Synchronization on Opera GX

Finishing with below bookmark selection in Opera GX

Items Online:17

Archived:0

Trashed:235

In Your Browser:17

Let me know if this help. 

Next step is Restore Original backup....

Also found that  Enable auto sync(every 60 minutes) even thought this feature is on it does not update either in Opera or Brave. I do a folder move on bookmarks and they don't sync to the addon or to web