Time Machine hasn't backed up to my external drive since 13/09/21 although set to automatically back up hourly etc

Just spent over an hour with Seagate support how confirmed that my external 2 TB Drive is connected, working and not full. They suggested I contact Apple support.

The only thing I can think is that back up failed around 13/07/21 around the time I had a blip accessing Pages & had to reinstall Chrome.

Currently I have set up the external hard drive again and Time Machine preference is showing 1.0 TB of 2.95 TB available, but has been waiting to back up for over an hour. Time machine on the menu bar also says waiting to back up. When I try to enter Time Machine nothing happens. Same when I press the option key and try and verify backups. Help!