Unable to compatibly downgrade 11.8 collation/charset behavior to match that of 11.4

I'm hitting an illegal mix of collations with existing client application code and data that is not (in a practical timeframe for this) changeable.

Illegal mix of collations (utf8mb3_nopad_bin,IMPLICIT) and (utf8mb4_0900_ai_ci,COERCIBLE) for operation \'=\'

The table has utf8mb3 and utf8mb3_nopad_bin on it. I've tried setting

character_set_server=latin1

collation_server=latin1_swedish_ci

character_set_collations=utf8mb3=utf8mb3_general_ci

to get the variables to match what I'm seeing on a connection to a pre-upgrade 11.4 instance, but still getting the error with no real change in behavior. Have tried a variety of other combinations/settings as well, with no real results.

I did NOT try fully disabling the client character set/collation negotation - that seemed like it could have potential, but also seemed like a horribly aimed sledgehammer. (Compared to that, leaving the instance on 11.4.x is probably preferable at least for now.)

I fully admit this is bad client code, and bad data already in the table, but I'm just looking to find out if there is any way to configure an 11.8 instance to match previous behaviors - i.e. am I missing something else that I should be setting server-side?

Open to suggestions here, but the key is it's impractical at this point to change the client side of this - that's a much larger scale problem to tackle.