how to remove a volume from Time Machine backups?

Thank you. I’m not sure if this helped, but I did do it. There is no option to turn TM on or off in the new OS. When I restarted the Mac and opened Time Macine preferences, the exact same configuration was there. So in frustration I clicked on the backup I’ve been trying to delete - and there was no indication I had selected it, no highlight on it of any kind - and then pressed the delete key on my keyboard. Surprise, a window appeared asking if I wanted to delete the selected disk - without being sure which disk it was referring to, I said yes and it immediately disappeared and the Add or Remove a Disk appeared as it was supposed to. So, success.

I do wonder if TM was confused by the external drive being partitioned. The reason I wanted to delete this second backup was both partitions werebacking up the entire hard drive and it seemed redundant. Now my main backup is backing up both partitions. Much simpler.

Thank you you for your help.

Ok, but just to be clearer, I am not trying to exclude a volume on my hard drive (which is partitioned into two volumes). I discovered that by not excluding anything the Time Machine backup defaults to backing up both my volumes to the first (main) backup on my external hard drive. What I'm trying to do is disable the second backup I set up on my external hard drive. It is one of several Time Machine backups listed, covering multiple external hard drive I back up to.

Thank you for your reply, Old Toad.

This is what my Time Machine Preferences looks like. There is no scrollbar, and no option to add or remove any of these green time machine disk back ups. I would like to remove the bottom one which is hard to even see here. If I double click it it will move up, but no other choices are beneath it. The Options button takes me to the Exclude window, but I am not trying to exclude files from a backup so that is no help.

No, I did manage to delete the backup as I explained above, by just hitting the delete key. I don’t know, it might’ve worked before but I didn’t think to try it then. No need for safe mode, the disk I didn’t want has disappeared and I have successfully backed up my hard drive to the main external desk, as I wanted to.

Yes I did do that, thanks.