Hello,
I understand you will have a infrastructure problem. Your experience will help some other !
About maria Db 10.4, I am not installed and I am 10.3.x currently (recommended for installation).
The test are been on ubuntu and debian, use mariadb 10.3.x by default if I remeber well.
I make some mistake like that and I do not understand why a software can not work. If the infrastructure is too old not work, if you use something too new, also.
About the index Undefined index: ... , it would be resolved on the next release. A big go work has been made on that to respect the strict mode of php. In this case it's better to include reduce that.
Normally it's inside the code (includes/application_top.php) I think or change in php.ini
If your experience can help to create a better documentation,it's good for everybody.
.