Hardware/software to segregat/secure a server on a local network

Hi

I'm sorry in advance if this is not the correct channel to be asking this question but I feel the expertise of this community would be best suited to this question.

I am an currently running a Linux server that hosts a VPN, DNS updater and webserver. Because there is a VPN running on this server I am wanting to segregat these services from the local network it is running on so that it can be used to a "commercial" standard (allowing trusted people to use the VPN but knowingly increasing the chances of malicious attack)

I have looked into software like ip tables and router DMZ but I just don't have the complete understanding of how it works and so would prefer to physically separate the server on the local network. This is my question, what hardware would allow me to do this? I am still open to securing the network using software if there is a suggestion.

Current hardware in chronological order: ONT (modem) Router (not very smart) Managed switch with VLAN capability (not using VLAN) off this switch is all local network devices including the server.

Any help/thought would be greatly appreciated. Any links to youtube tutorials also.

Thanks, Jacob