How to access back up of old mac (old iOS) on a new mac

I have a Time Machine back up of an old mac on a hard drive, but am unable to view it. I think its because my new laptop has newer iOS software? Not really sure. I want to be able to go into the back up and selectively save just some photos & videos.

I know how I should be able to do this, as I can do it for the Time Machine back up of my newer laptop. It's just the old laptop that I can't access the backed up files for.

I'm kind of panicked that I can't access any of it as my old laptop has pretty much completely packed up so I'm worried I won't be able to save them from there.