I know that it would be better to use a switch, but I would need a 10Gbps (or 2,5Gbps, do they exists) switch with 2 sfp+ port (1 for Internet connection and the second one for the server). In this way I've just bought the 3 old NIC for 25€ and that's it. I know that they will consume way more than the switch, but how many years do I need to break even?
I've just edited the original post to make clear that Proxmox has nothing to do in this picture, it just is installed in the same PC where the NICs are.
What I need it just assign 6 VLAN (tagged, coming in from enp2s0) to 6 NICs (untagged to: enp9s1f0, enp9s1f1, enp9s2f0, enp9s2f1, enp10s1f0, enp10s1f1).
I don't need to assign VLANs to VMs, I need to assign them to 6 phisical NICs (tha fact that they are installed in the same machine where there is Proxmox is irrelevant).
Forget everything that I've written, I just need to assign 6 VLAN (tagged, coming in from enp2s0) to 6 NICs (untagged to: enp9s1f0, enp9s1f1, enp9s2f0, enp9s2f1, enp10s1f0, enp10s1f1).
Well, it's a Wireguard client that connects to somebody else's server!
I prefer not to let that "somebody else" enter my network.
Since it's pretty easy, I run my own Wireguard server!
This would also lead to safer cars because they are better roadworthy
Well, I'm not sure about this literally about car and figuratively about selfhosted: not all the selfhoster have the skills to selfhost, they just think they have and so for the car. If you screw up a service/the whole server you may lose all your data or be at the mercy of some data kidnapper, if you screw up your car brakes, well...bye bye.
In both cases, we don't have enough skilled people to have that 25% selfhoster (but not even one tenth) nor 25% car self repair drivers. And this is not as bad as it sounds: we can't be skilled about everything that we need, it's just impossible! And that's why we have society!
Use a VPN like Wireguard.
I'd suggest putting the laptop into a DMZ, if you have a good router.
If you don't...buy a 30/40€ Fujitsu Futuro S720/920 and use It as an OPNsense router (video tutorial)
OPNsense is in one PC (and it only works as router/firewall), Proxmox is on another PC with all the NICs and Proxmos and it will also work as switch.