bgoble wrote:
Time machine backup:
I have a new MacBookPro to replace an old one I was backing up with TimeMachine on an external drive. If I begin backing up the new one on the same external drive, will I have access to files that were on the old computer hard drive but no longer on the new one's hard drive?
Holding the Option key and clicking the TM icon in the upper right menubar>Browse Other Backup Disk — see if it presents options here.
If your new Mac inherits your backup history - Apple Support
https://support.apple.com/guide/mac-help/if-your-new-mac-inherits-your-backup-history-mh35732/mac
Enter TM and then use the keys Shift Command C This will bring upfront your main drive. You can now scroll back in time. Once you get where you want you can then open the drive and scroll down to your user library and then documents, downloads, etc. and find the item you want. Then copy to desktop and use or move from there.
ref: How to access Time Machine files from previous OS install?
https://discussions.apple.com/thread/5579823
If you get a replacement Mac, you probably want the Inherit or Reuse option.
If you get an additional Mac, you probably want the Create New Backup option.
ref: http://oldtoad.net/pondini.org/TM/B5.html