Illegal mix of collations (utf8mb4_unicode_ci,IMPLICIT) and (utf8mb4_general_ci,IMPLICIT) for operation ‘=’

I am guessing you have different collations on the tables you are joining. It says you are using an illegal mix of collations in operations =.

So you need to set collation.
For example:

WHERE tableA.field COLLATE utf8mb4_general_ci = tableB.field

Then you have set the same collations on the = operation.

Since you have not provided more info about the tables this is the best pseudo code I can provide.