I am upgrading a site to Joomla 4 from 3.12 . The magz_ii template worked with Joomla 3.12 but after the upgrade I get the Error 500 behavior::modal not found page. The default template Cassiopeia works.
Unfortunately the site is on a hyper-v machine on my home computer so I can't give direct access to it.
Any clues as to where I can look to find the problem?
It is a copy of a site that has been around for a while with many Joomla upgrades over time. A car club site and it would be a nightmare to try and rebuild it from scratch.