user_update_9301 fail during update from D8 to D9

Are there other primary keys on that table, besides uid?

Many sites have upgraded to Drupal 9 so I suspect the steps to reproduce are incomplete.

The keys I see for the "users" table are :

• uid
• uuid
• langcode

I agree that they must be some differences that cause this problem, but as for steps to reproduce I can't give others (this is all that I did).
Maybe there was something in the old site structure that can cause this problem ?

Is one of those a primary key?

Only the "uid" one

What is the key's name?

It's "uid"

Here are other reports of the same:

• https://www.drupal.org/project/drupal/issues/3255419#comment-14691565 🐛 Updating to Drupal 9.3 fails when sql_require_primary_key MySQL system variable is ON. Fixed
• https://www.drupal.org/project/drupal/issues/3275916#comment-14691557 🐛 user_update_9301 fails again Postgres14 durin upgrade Active

I have explored all solutions proposed on the thread you shared, all the patches proposed seem to be already applied in my core files (I didn't check the mySql files since it's not my case, obviously).

I also checked the tables views and sequences in my database, all have the same owner (so it's not the origin of the problem)