How to fix the sys.host_summary table in MariaDB 10.3.13
The sys schema is not bundled with 10.3, but seems to be planned for 10.5. If you don't use/need it, you can safely remove it: DROP DATABASE sys;. If you do need it, you need to try resolving the issue outlined in the error message. For a start you can do SHOW CREATE VIEW sys.host_summary; to see which tables, views and functions it's referencing, as well as the definer/invoker.