Can't override sublayouts

[SteP[IT]]

Hi all
I have installed latest VirtueMart4.0.20_Joomla_3.10.11-Stable-Full_Package.zip build, then upgraded to latest Joomla 4.x (this is why I need to get the latest Joomla version running to use other plugins in the final site).
But I'm experiencing a issue in sublayouts overriding: I need to add some further schema.org fields in snippets,php results (i.e. the Brand logo, not included in orginal snippets...), but when placing the override inside the usual html theme location it doesn't work (all other overrides are normally working).
Is there any known issue for this behaviour?