How to free up space on backup drive

I use a WD external to backup my 27” IMAC Catalina OS but I recently upgraded to a Mac M1 and want to clear enough space to start backing up my M1 but want to save at least one IMAC backup as I still have that Mac. My WD is 1TB and I deleted 6 of 7 IMAC backups in order to open some space but nothing changes and I don’t have enough room to backup my M1. No matter how many IMAC backups I delete, my WD still shows 50.1 GB space available which isn’t enough to complete an M1 backup! I tried shutting down, unplugging the WD and re-starting but nothing works - always 50.1 available! What am I doing wrong???

Hi @webbsk8r
Have you opened a Support Case? If not opened, for more information, please contact the WD Technical Support team for the best assistance and troubleshooting:

Apparently nobody at WD Support reads my requests thoroughly enough to understand the issue - one told me to reformat my drive and that would work (No, it would lose my last backup), another said it appears that deleting the backups on your WD did not release any space on your Mac M1 (I wasn’t trying to release space on my M1, but I did want to release space on the WD backup)! I’ve sent two requests with a long-winded clarified explanation on the second one and got a reply to make sure I emptied the Trash on my M1 as that may be the problem or else I could reformat my WD drive - I did, it wasn’t, I don’t want to reformat my drive unless I save the last IMAC backup!. This is very frustrating! I’ve worked in IT for 20 years and I understand my dilemma, why can’t they do a simple read???