Just after setting the template, we are receiving this:
Looking for advice to resolve it?


Template Name:Business
Joomla Version:4.2.5

Looks like you upgraded from J3 to j4 and didn't previously deactivate or delete plugins that no longer work on J4 PHP8. Roksprocket must also be completely deactivated or removed.
Take the debug mode and find the plugin, there is the way in german language:
forum.joomla.de/thread/6467-fehler-finde...ug-modus-call-stack/

Nope!
This is a fresh start.
I'll check the link anyway.
Thank you.

Then test the following:
Is the JP template specified as the default in the backend?
Is the Astroid plugin activated?
Did you also assign the template in the menu to your home page?
What happens when you switch to Cassiopeia J4 Standard template?
Did you use quickinstall or just install the template without sample data?

I wish you success!

Is the JP template specified as the default in the backend? YES
Is the Astroid plugin activated? Now, I installed Astroid. And the error is gone. Thank you.
Did you also assign the template in the menu to your home page? YES
What happens when you switch to Cassiopeia J4 Standard template? It works.
Did you use quickinstall or just install the template without sample data? I just installed the template. What are the proper steps?
Thank you.

Nice that it works now.
The template will help you if you are still inexperienced. Then you already have example data and can adapt the existing structure according to your wishes. Otherwise there are no technical advantages.

I'll set your topic to solved now.