Probably i am coming a bit late to the party ;-)
While updating the rompr docker image i noticed the error 'Specified key was too long' when using mysql. (mariadb)
This is because UTF8mb4 allows max varchar 196 instead of 255.
I found i had to add
innodb_file_format = BARRACUDA
innodb_large_prefix = ON
innodb_default_row_format = DYNAMIC
to my INNODB Section.
Might be worth adding to the documentation.
Cheers Tom