Hello esophoria,
We understand you're having issues accessing your News+ subscription on your Mac since updating to macOS Big Sur. We'll be happy to help.
Thanks for checking that you're signed in with the same Apple ID on all devices. To clarify, if you go to System Preferences > Apple ID does it show that News is enabled for use in iCloud? Also, if you go to System Preferences > Apple ID > Media & Purchases, does the Apple One subscription including News+ appear here as you'd expect?
Keep us posted on what you find out and we'll go from there! For more info on getting your News+ subscription on all your devices, check out:
Get Apple News+ on all your devices
Take care.