mysql_upgrade fails without providing any meaningful diagnostics

after upgrading to 1.4 from 10.3, I execute mysql_upgrade and I get
mysql.user OK
Phase 4/7: Running 'mysql_fix_privilege_tables'
ERROR 1071 (42000) at line 437: Specified key was too long; max key length is 1000 bytes
FATAL ERROR: Upgrade failed
But, that is mariadb upgrader code that fails, for my server does not have a single innodb table, all are Rocksdb. If I start Mariadb with skip-innodb=1, there is no error, therefore, the error happens with the upgrader tries to create performance tables for inndb.
if this is a table from mysql then a descriptive message should say what table is the offending one. I tried to trace all activity and the last message is:
36 Prepare DROP DATABASE IF EXISTS performance_schema
36 Query EXECUTE stmt
36 Execute DROP DATABASE IF EXISTS performance_schema
36 Query DROP PREPARE stmt
36 Query SET @cmd= "CREATE DATABASE performance_schema character set utf8"
36 Query SET @str = IF(@broken_pfs = 0, @cmd, 'SET @dummy = 0')
36 Query PREPARE stmt FROM @str
36 Prepare CREATE DATABASE performance_schema character set utf8
36 Query EXECUTE stmt
36 Execute CREATE DATABASE performance_schema character set utf8
36 Query DROP PREPARE stmt
36 Quit

so what comes next is generating the error. How do we know what code is being applied?