Sequoia: End of recovery from Time capsule backups?

I tried to upgrade my 2TB Macbook Pro 2019 to Sequoia 15.0 . Unfortunately I also checked before the upgrade to save the folder Documents to Icloud drive. This was the error and the Mac started to heat with process fileproviderd and cloudd which did not stop for hours. After forcing to halt the Mac and calling the Assistance, I realized that the former Documents was spread into at least 3 places, the biggest being in ~/Library/?? purgatory/??/Documents . But about half of a Terabyte was lost. I decided to use the latest backup from late August to restore it.

Unfortunately, the Assistant Migration doesn't work anymore on a Time Capsule, because if you know all the passwords related to your Time Capsule and did not crypt the backup (you can verify it with Finder), Migration Assistant recognizes your Time Capsule but when you click on the icon, it asks you to enter a password which you never set and therefore doesn't exist.

I spent a lot of time with Apple Assistant (resetting the Time Capsule etc) and they said that Apple will not fix that bug because the Time Capsule is too old.

Yes the material is old but the backups are not. And there is no warning before upgrading.

-1- If you know more on this strange password, please tell us.

-2- If you need to know how to restore the Time Capsule backups by using a fast SSD external drive, I can tell you.

It lasted one day and half (for 1.5 TB) to copy from the Time Capsule via the WiFi to this external drive. A newer Time Machine with such a second and fast SSD USB-C drive lasts 2 hours only. But I had to buy two very expensive but fast SSD USB disks.