I cannot replicate this in Joomla 4.0.3-dev/PHP8.0.10

I:

• Duplicated "Cassiopeia - Default" and called it MINE and before saving made changes like turning off brand, changing the colour theme, and enabling the three options

I also set it to default and saved:

Then I logged into the frontend as a super admin and tried to edit a module and I was CORRECTLY given my new style

I then tried the profile edit page index.php?option=com_users&view=profile&layout=edit and again got the right customised template style.

Module edit would use the style of the page that you are editing the modules on.

In my test (just like @PhilETaylor ) if i edit the modules on the home page the template style used is as expected the template style of the home page and if I edit the modules of another page that is using the default template style then its is as expected using the default template style.

Pages that have no menu item at all (unless created) will always use the settings of the default homepage. That would include the template styles and modules.

Module edit would use the style of the page that you are editing the modules on.

In my test (just like @PhilETaylor ) if i edit the modules on the home page the template style used is as expected the template style of the home page and if I edit the modules of another page that is using the default template style then its is as expected using the default template style.

Pages that have no menu item at all (unless created) will always use the settings of the default homepage. That would include the template styles and modules.

Ahh so it is expected behavior. But this creates (depending on the type of settings the template has) profoundly different user experience determined by the page the module is edited on. Is there a way to prevent this behavior? I mean even a snippet of code to put in some template override.

You could take a look at this free plugin https://extensions.joomla.org/extension/clean-edit/

Set to "closed" on behalf of @jwaisner by The JTracker Application at issues.joomla.org/joomla-cms/35465

Closing as this is expected behavior.