Cannot have a CiviCRM-link menu as default (home) page
In Joomla you declare one menu item to be the default "front page" i.e. the one that you get to when no menu is selected, only the web sites base path.
In J3 this also worked for a menu entry that was a CiviCRM-entry, such as Event Listing or Mailing List Subscription. (check e.g. https://events.responsive.se which is a J3 site with Event Listing as the default menu entry.)
With J4 this no longer works. When going to the "home page" the menu item is highlighted to indicate that it is active, but there is no output in the content area.
I tried this with a clean J4 and CiviCRM and see the same thing. The underlined "Subscription" indicates that it is the menu entry that is active.The J4 default template Cassiopeia displays breadcrumbs which strangely enough shows "Home" and not "Subscription" (which is the menu entry for CiviCRM Mailing List Subscription form).
This is extra strange because the breadcrumb for the Home menu entry is actually "Home/Home" so the default page Subscription is something in between...
Explicitly clicking the "Subscription" menu entry correctly shows the form.
I don't really know enough about Joomlas routing to understand where the problem really is, but I'm starting by reporting it here.