Have raw pbundle data on drive, need it to be recognize as time machine

Question

So I made a home-brewed linux / raspberry pi time machine more or less like this. I ended up with time machine data stored on an ext4 partition shared via samba that was successfully recognized and used as a time machine backup destination my my mac. The drive holds 3TB of information, so it's full of something.

But when I tried to use that drive as a source from Migration Assistant after my mac was wiped by apple repair, it won't recognize the network drive.

So I bought another 6TB drive, formatted it as HFS, and copied the .pbundle / sparsebundle file onto it. I thought of this as a "nuclear" option sure to work.

But now, the mac still doesn't see this new drive as a time machine source.

What should I do? How should I recover my data?