Thanks for the quick reply.
Correct, the tables 'mlf2_akismet_rating' and 'mlf2_b8_rating' as well as 'mlf2_uploads' exist in the database.
You had obviously installed a version from the 2.5-branch (2.4.99.x or a 2022-any-number) before the current update attempt. You might have downgraded the version to a stable version of the 2.4-branch but the then obsolete tables remained.
I don't remember doing that. But it doesn't matter how the tables got into the database.
My question: Can I simply delete these 3 tables, for example with phpMyAdmin?
As you are running MLF in version 2.4.24 again, you can delete all tables, that are generated for version 2.5. These are the tables for uploads, B8-wordlist and rating and the akismet rating table.
Database error in line 304: Unknown character set: 'utf8mb4'
What version of MySQL operates on your server?
I cannot say with certainty, in which version of MySQL the charset utf8mb4 was added but in case of MySQL 5.0 would be not able to handle the charset utf8mb4, you will not be able to upgrade the forum script to version 2.5 or any newer version. On the other hand MySQL 5.0 is a really ancient version. Please ask your hosting service/server admin to upgrade to a recent version of MySQL.
Trenne niemals Müll, denn er hat nur eine Silbe!