Joomla needs at minimum 8 characters for the password length. That's expected behaviour. If I understood your issue wrong please reopen the issue.

I agree on the choice of 8 characters but then, when migrating from joomla 3 to joomla 4 this parameter must be automatically changed to respect the criteria that the CMS itself wants and verifies.

i don't think so...
the site admin should do a deliberate choiche not the end user
i still run a migrated site from 3 to 4
with the same psw
please don't kill me , i'm lazy ;)

I had the same today.

I migrated a Joomla 3 website to Joomla 4.
The password length was set to 6 in Joomla 3.

When I wanted to add an email domain to the users, I kept getting the message of password length is not correct.

I did not understand that and after a consultation on mattermost we came to the conclusion that the length should not be 6 but should be at least 8.

Please note that this is not stated in the message.
You only see that something is not right, but you do not see what is not right.
The message must then be that the length must be at least 8.

Translated from Dutch with Google

The point is that it comes up when you adjust the options and want to save.

The current passwords are separate from this