My system upgraded from MySQL 5.7.30 to 8.0.
After that, CiviCRM was broken and I had to downgrade. I did it to Mysql 5.7.31 and the database ran again, but with a bunch of identical error messages at the top of my pages:
Notice: Trying to access array offset on value of type int in element_children() (line 6656 of /usr/share/drupal/includes/common.inc).
I still have to perform some upgrades from CiviCRM 5.26.0 to 5.30.0
My additional question is: is it sufficient to upgrade CiviCRM to make the errors disappear or do I have to fix first the errors. In case I have to upgrade, I would like to know if it is better to upgrade in one shot from 5.26.0 to 2.30.0 or will I do it step by step?