While you can host web sites with OMV, it is a NAS. If you need multiple versions of php, docker is the best way without potentially causing issues with OMV.
i host exactly one website on my NAS: nextcloud. Nextcloud wants a more recent PHP version to update to a more secure Version with more and improved features.
PHP-FPM is an absolutely great way of offering different PHP-versions. e.g. Plesk does it that way, too
Docker is NOT a good way of doing this, It's just a bit too much effort (a container with own virtual network NATing, with another nginx that cannot be administrated from the OMV GUI, with php, that's not integrated with the systems package update system...) when it can be achieved by a technique that is already implemented. Just give us an option to choose one of the installed PHP-FPM-versions.
if OMV is just a NAS, then why does it have an nginx-plugin? Why does it have Docker? No NAS i can buy of the shelf has docker.
please accept: OMV is a management tool for a debian based homeserver and not only a NAS (of the shelf Consumer NAS have become more of a home server. compare the feature set with a professional NAS yourself. )
and please accept: when people ask for different PHP-versions they probably need it. For testing, developing, or simply for different webguis or just because the version offered by the OS as default is outdated.
And OMV itself could do with less dependence on singular Version and a more modern PHP-Version. Performance and security have greatly increased since 7.0.
don't get me wrong: OMV is a great software and I appreciate the effort you do in developing and supporting this software, but not listening to reasonable requests of actual users, not offering an update path from OMV 4 to 5 is making me shift away from OMV
