So we're hosting our own minecraft server and a suitable connector for cross-play - and it's easy to join on tablets, computers and so on because there's a button that allows you to enter an address. But on the switch, Microsoft in its wisdom decided that there'd be no "join random server" button. But there are some official realm servers, and they just happen to host a lobby and the client understands some interface commands sent by the server (1). Some folks in the community devised a great hack - you just host a lobby yourself that presents a list of servers of your choice. But to do that, you need to bend the DNS entries of a few select hostnames that host the "official" lobbies so that they now point to your lobby. Which means you need to run a resolver that is capable of resolving all hostnames, because you need to set it in the switchs networking settings as the primary DNS server.
Now, there are people that run resolvers in the community and that might be one option, but I'm honestly a bit picky about who gets to see what hostnames my kids switch wants to resolve.
Whitelisting networks is impossible - it's residential internet.
The reason I'd be interested in running this behind a VPN is that I don't want to run an open resolver and become part of an amplification attack. (And sadly, the Switch 1 does not have a sufficiently modern DNS stack so that I can just enable DNS cookies and be done with it. The Switch 2 supports it).
Sorry if this sounds complicated. It's just hacks on hacks on hacks. But it works.
(1) judging from the looks and feel, this is actually implemented as a minecraft game interface and the client just treats that as a game server. It even reports the number of players hanging out in the lobby.