@Moonbase59: thanks for your feedback.
1st off: yes, I did add cssclass: clean-embed in the YAML, and I did enable the snippet after restarting Obs.
I tried the Help file, but am not sure if I did it right.
Since it works at your end I must be doing something wrong.
I created a new folder snippets in Librar/Application support/obsidian/Obsidian Help.
Then I added your snippet, restarted OBs, and enabled the snippet in the Help vault’s settings.
I created an embed myself. But there was no effect.