Frontend Details Problem

Hi
We recently moved our site from Joomla 4 to Joomla 5. Since then when the details button  is clicked on a frontend download,  the page that opens has no site formatting ie no menu's breadcrumbs etc  This can be seen by clicking the Details button on this page mr2oc.co.uk/downloads/club-stationary The result is the same whether logged in or not and on 3 different browsers. Fairly sure it used to open in a popup not a full page,  certainly wasn't as it is now. Any idea's ?
Regards
Jimi
Edit
Related to this is there any easy way to hide the Details button ? as it's not really needed in our setup and would remove the problem 

Hi Jimi,
Thank you for your message and for describing the issue after your site migration to Joomla 5.
If you wish to hide the "Details" button, you can enable the configuration option "Hide Details Button" in Configuration → Tab: Themes. This will remove the button from the frontend.
However, if you still want users to be able to view document details, please try disabling the option "Show Document Details in Popup" (also found in the Themes tab). This may help resolve the formatting issue you described and adjust how the details are displayed.
Thanks
Dam

HI Dam
Thanks for that, I totally missed the "Hide Details Button" option     I tried the option "Show Document Details in Popup" both ways but it made no difference. No matter I've hidden the button.
Regards
Jimi

OK Jimi