Increase share of external hard drive allocated to Time Machine

As a first time user, I just followed the prompts. (Using a recently purchased M1 Max MacBook Pro refurb on a WD 8TB Easystore) A prompt popped up asking me how much of the 8TB I wished to reserve for Time Machine. I used a proffered slider to select 3.5TB. I was surprised and thought that to be a very neat feature; although a tech at a local Mac repair shop had never seen it either. However, now that I'm questioning that my choice of 3.5TB instead of the whole disk (since I have other external storage too), I see in Disk Utility that there are no partitions and it appears that Time Machine considers it all open territory, so I'm mystified. Not unhappy in this case, but if I hadn't changed my mind, I'd be pretty disappointed in a fumbled feature that appeared to be pretty clever in Time Machine.

Yep, I think you're right. The whole thing is puzzling, though. Apparently, this is such a new feature in Time Machine that few have seen it, and it obviously is buggy as it was unable to lock in a specific usage maximum of the full drive.

Very interesting! Thanks for that info. I didn't even think about having it back up my 13.3" M1 MacBook Air as well.

I have just gone forward as is, assuming Time Machine owns the whole drive. If it functions as it claims, I'll love it. Won't have to tend to it for quite a while, I think.