I updated to Joomla 4.1.5 and updated the T4 plugin, then I installed DP Calendar and made a menu item for it. Now when I try to go to the template to make changes to the default template, the icon to edit a template is gone, I can only copy it which doesn't do much good because you can never get to edit it. I don't know if this is because the issues associated with updating the T4 plugin (which never works, ever ever ever on any Joomlart template!) or if the template has a problem. In which case I will be unable to update the T4 plugin for the life of the website.
I do have an Akeeba backup to do a restore from, and will do so after you've had a look at what has happened. Perhaps you have seen this before and can tell me if this can be fixed. I was trying to change the default masthead image to something other than the gray patterned image currently showing when you select Calendar from the main menu.