As stated in the error it's a PHP compile error and has nothing to do with the browser or a firewall.

So I guess the declaration of the class property is wrong and throws an error - at least in this PHP version:

should be declared as 


The problem is, that this J-Installation is on a infrastructure of a university and I have only access to the J-Backend. So no FTP or hosting panel with file browser/manager to change the code.

Please update to PHP 8.x or use Astroid 2.6.x.
Astroid 3.x is running only on PHP 8.x
..
And its not a missing string coz before "mixed" shouldnt be a string.

Then I must have misinterpreted the error message and PHP documentation - apologies for that

With Astroid 2.6.x I can now edit the template options - thank you.

But the template itself no longer works (I guess because the latest template version is too new for the framework). After changing the template option, I had to reinstall 3.0.14 to get the site working again.

Aren't there mechanisms (preflight-script or similar) to prevent extensions that are incompatible with the PHP version from being installed at all?

However, I managed to do it. I only had to change the mobile menu for one template style. Too bad it turned into a two hour task (and it also took your time).

But all in all, great and fast support here - thank you very much.


Roger

Yes youre right.
But please update to PHP 8.x to fix all issues