How to integrate two backups into the internal drive ?

You can’t truly merge two Time Machine backups into your internal drive automatically, macOS doesn’t support that. The clean way is manual, once you find the newer backup (the 10/28 one), mount it in Finder, then manually copy only what’s missing or newer than what’s on your Mac now. Use Finder’s Replace/Keep Both prompts to decide file-by-file, or use a tool like ChronoSync or Carbon Copy Cloner for a more guided comparison and sync. They’ll show differences between drives and let you merge data safely without overwriting newer files. After that, ditch the old failing backup disk and start a fresh Time Machine backup to avoid this mess again.

RAMSLOT wrote:

Nope. My bad. B/U. #1 is from three weeks ago. B/U #2 more recent not yet found. Data was added into the IHD since B/U #2. IHD restored using B/U #1. How to make a complete B/U in the IHD when B/U #2 is located,

Feel free to ask more if clarifications needed. (I've now set-up TM backups attached to router.

Two incomplete / corrupt backups is always going to mean some (manual) re-assembly is required.

If your internal storage is not corrupt (and you don’t need to restore, or only need to restore specific lost files), then rescue what you need, scrap the old backup hardware, and start fresh Time Machine backups.

It seems to me if you found a more recent backup you would want to restore that vs. the older one. No matter though, if you restore items that already exist on the source TM will present a dialog with three options:

So to confirm, you have a failed backup drive with the latest backup, and a corrupt internal SSD running macOS 14?

I’d first have a look at the backup HDD, checking to see if it’s the HDD that is failing, or the enclosure.

If the latter, then swapping the HDD into a different USB sled is usually feasible.