No BE login after upgrade 10.4 to 11.2

FE is OK.
BE after Bootstrap login screen :
object not found 404 error.
runs correctly with downgrade back to 10.4.

I have a similar issue, although neither FE nor BE are working…
Composer installed 10.X upgrade to 11.X - doesn’t work (not found 404 error or missing site configuration etc.) and when installing a fresh typo3 11.X version installation ins stuck in step 2.
I opened a topic as well, maybe those issues are linked/related.