yono-senada94 Based on your post title:
pixel 4a 5g tmobile worked the first month, now wont update
The Pixel 4a (5g) is end-of-life, it will no longer receive firmware or most driver security updates and will only receive extended support from GrapheneOS as part of the main releases with all GrapheneOS changes including all of the latest Android Open Source Project changes.
Now based on the actual contents of your post (which feels unrelated to the title of your post):
aurora store says chain validation failed, my messages are scambled, the date time is wrong, updating says.....failed to check for updates.....an error occurred checking for the latest update chain validation failed....
So, just to clarify, your issue is not actually with GrapheneOS system update ("...now won't update"), but rather with a third party front-end wrapper, AuroraStore that gives you the error?
Edit: AuroraStore can be problematic, see https://discuss.grapheneos.org/d/8255-aurora-does-not-install-apps/8
aurora store says chain validation failed
Have you considered looking through AuroraStores issue tracker and/or asking them directly? https://gitlab.com/AuroraOSS/AuroraStore/-/issues
Edit #2: Split duplicate of https://discuss.grapheneos.org/d/13240-cant-update-or-install-app