Write to the person who makes it.
Questions, bug reports and ideas all go to the same inbox, and Simone Cerelli, who makes Twinmark, reads it.
Before you write
What Twinmark’s menu says, and what to do about it.
Not connected: open Chrome with this profile
Twinmark can only write to a browser that is running. Open that browser with that profile and it catches up by itself.
The extension isn’t connected yet.
Add the Twinmark extension from the Chrome Web Store in that profile. It connects by itself within a minute. If it still doesn’t, reload it in chrome://extensions.
Full Disk Access needed
In System Settings, go to Privacy & Security › Full Disk Access, turn on Twinmark, then reopen it if asked.
This sync removes many bookmarks
A safety brake stopped the sync and nothing has been written. If the changes in your reference are the ones you made, confirm. If they aren’t, put them right in the reference first.
Another Mac writes these bookmarks
Only one Mac per Google account writes, so nothing arrives twice. Press Use this Mac if you no longer use the other one.
I want my old bookmarks back
Open Settings › Backups, choose a date and restore it. Twinmark saves the browser as it is now first, then pauses syncing so you can check.