eM Client 10.3.4341 running on macOS Tahoe 26.2 Beta
When I start Theme Editor (either via “Tools → Theme Editor” or via “Settings → Appearance → Theme Editor”), it opens up in its window and then I get the Apple “Beachball”: Freezing.
Reproducible.
Also, I had it running for about 10 minutes, no change.
The Mac Theme Editor opening issue in OS 26 has been fixed in this new “Interim update” V10.3.4434 from Testing / Support where they identified the issue.
You can download the updated version at the link below:
Note:- Make a manual backup first before installing via “Menu / Backup” if you don’t already have regular eM Client backups incase you need to restore for any reason. You can see when the backup is complete in Show Operations via the dropdown on the right of Refresh top left.