All of my Mail.app emails now say "TO" is there a way to turn this off?

Easy to fix:

View->Hide To/CC label

EDIT: in reality the name does not change from Show to Hide and back, so it reads "Show To/CC label" and if it is checked, select it again to toggle it off.

sexykitten wrote:

Just started yesterday. Very annoying. Obviously emails sitting in my inbox were addressed TO me! Also affecting other mailboxes.

https://discussions.apple.com/content/attachment/ffcc72f4-9e6d-4211-8326-a9568d825ab9

what exact macOS is this?

sexykitten wrote:

It says Monterey 12.2.1 (21D62)

The current stable release of  Monterey  including bug fixes,  security updates macOS 12.6.9 - I would start there

Keep your Mac up to date - Apple Support