Critical Backup interrupted. How can I restore from a "backupbundle" file?

I need a piece of information.. was Time Machine working for days and weeks before you reformatted the disk?

If so you have multiple backups inside it. If this is the one and only time you have ever used Time Machine then you will have trouble. I am not sure you can recover.

A halted incremental backup from Catalina should still behave as they did in the past.. i.e. open the backupbundle in Finder.. which might be confused what sort of file it is so change the name to sparsebundle.

Inside the sparsebundle you should find an inprogress file. Normally we would delete that file which causes the backup to no longer work. Delete that at your own risk.. It is no bad thing to archive the TC before you start so you can always use the version on the USB drive instead.

Note you may need to be running Catalina to accomplish anything. Definitely you cannot access the Time Machine backup via Time Machine in Sierra.. you cannot ever go backwards.

Another thing to try without deleting inprogress or anything else is to boot to recovery in the laptop. Open Time Machine and select the backup.. if it works.. tell me if it doesn't because the name change could help. Go back to date before the backup got wrecked and it might be possible to then recover this backup to a separate USB drive.

Sorry.. perhaps I was not clear.. changing the date has nothing to do with the problem.

Here is the method step by step.

1 Boot to recovery.

You use Option + Command + R

I usually just hold down Option key when you hear the start chime from off.. and all the boot devices will show.. including Recovery.

https://recoverit.wondershare.com/mac-data-recovery/boot-into-recovery-mac.html?gclid=EAIaIQobChMIzNLoyv665QIVyB-tBh1ZLQ50EAAYASAAEgIhlPD_BwE&gclid=Cj0KCQjwrIf3BRD1ARIsAMuugNt971CJmhKemBRN1GOtEDyRZ5FI4-qw6ymWOO82wIjnGWJ6GwNuU6MaAvMdEALw_wcB

2 Start Time Machine which might be called Setup Assistant.. not sure lately as names have changed.

It will allow you to access the Time Capsule and try and find the backup. If it opens.. then you are presented with date you wish to restore to.. This is the date I am tell you use.

Please read a much earlier post I did on using both Recovery and Migration tools. It is a long thread so please do spend the time to read the whole thing. Even if somewhat out of date it should help you.

https://discussions.apple.com/thread/7236090

There is a picture from this with the title above it..

Pick the date. Skip to ones before the failure.. maybe a few days.

3 If you cannot open the Time Machine backup here you will need to rename it to sparsebundle from backupbundle. All versions of Mac OS TM used Sparsebundle until Catalina when it changed.. Apple has given no explanation of why.

4 Then restore this version of the boot drive to a different disk. I suggested a USB drive plugged into the computer so you don't mess up the current install.

If the above doesn't work at all, then delete the inprogress file from inside the backup.

https://www.fireebok.com/resource/three-ways-to-remove-inprogress-time-machine-backup.html

In the same post I did there is a picture showing the inprogess file you need to delete.

This file will often block the Time Machine backup being used.

TM cannot see the file at moment.

TM in Sierra cannot open Catalina version TM file..

But in Finder you should be able to open it after you change the name.

And remember to archive first.. before you start messing around otherwise you could damage the TM backup beyond recognition.

But for that, step 4, how do I "restore this version of the boot drive (the USB)"?

You are not reading the other thread carefully enough.

Here is the relevant portion. Remember this is Time Machine inside recovery.. NOT from Sierra install. It must be done from recovery.

Pick the date. Skip to ones before the failure.. maybe a few days.

Now here is the key to this.. you get to select where you will recover to.. you are going to recover to the USB drive. Don't mess up your internal drive.

Then away you go.