Database error when saving CiviCRM event: “Row size too large”
this might be a mariadb config issue. 

# enable large indexes and Barracuda
# for utf8mb4
innodb_file_per_table=1
innodb_file_format=Barracuda
innodb_large_prefix=1


might also change the tables to
ROW_FORMAT=DYNAMIC or ROW_FORMAT=COMPRESSED
see this post for much more info on this front https://stackoverflow.com/questions/15585602/change-limit-for-mysql-row-size-too-large

but do not follow the suggestion there to alter the tables to use MyISAM instead of INNODB, that's a really bad idea.