cannot browse time machine after fusion drive removal

I have a 2019 27in iMac which had a "1TB" fusion drive and all was right in the world except for 5-8 minutes to boot. It's been this was with both Big Sur and Monterey OS's.

A few weeks ago I removed the fusion drive ssd component and replaced it with a 480GB SSD to house the MacOS system. The existing 1TB drive was reformatted to be used as the user data "Home" area.

After the upgrade the User Options were changed to use the old 1TB drive as the user area and everything has been working perfectly.

NOTE: there is no longer a fusion drive "core storage" system in use. I specifically did it this way.

I have since done the same to my partner's identical model iMac (as her boot times were worse than mine).

We both have simple external USB drives plugged into our Macs - being used for Time Machine.

Both iMacs were restored from their respective Time Machines after Monterey was reinstalled... all good.

The problem: (which she just noticed)...

Time Machine seems to be working ok.

(eg. in Finder I can browse to my external drive, which is: /Volumes/TimeMachine-CB/Backups.backupdb and I can see it all happening chronologically.... so far so good.)

If we "Enter Time Machine" on our iMacs then it looks like it's correct and there is a couple of years of dates on the slider on the right of the screen.... but can't select ANYTHING (even since the hardware upgrades).

UPDATE: on my iMac I checked the ownership of my .../Backups.backupdb and found I was not listed and neither was my group. (Get Info > Sharing & Permissions).

Just for a giggle, I specifically added myself and gave myself full read/write permission....

now my "Enter Time Machine" interface allows scrolling to any historical point, however my Mac is still applying permissions so I can't as yet see old files.

Has anybody else had this Time Machine interface problem?