Fixed by Microsoft as of Feb 23rd, 2023.
https://support.microsoft.com/en-au/topic/error-when-opening-actionable-messages-be7b8154-f293-4784-a3d9-08bef7f4c36e#:~:text=In%20Outlook%2C%20the%20error%20message,open%20actionable%20messages%20is%20reached.
If a user receives this message, please look for 3rd party addins and either disable as necessary or repair them.