[User]

FWIW, I had this same issue. I use the WP plugin auto-update feature, not manual updates, but got version 8.9.5 (about an hour ago?). I was able to get around the Critical Error by renaming all of the plugin folders for Newsletter except the main one. Thanks for the update; once I upgraded to 8.9.7, I was able to revert the folder names and everything looked normal.

[Author]

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