Use encryption, using vpns for such a trivial task is a “really bad idea”
There are many cases when somebody wants to have their dns public, maybe they want to share with their friends, family, community, audience (not everyone is a solo server user)
Also, it’s good to use your dns even before connecting to the vpn. Just use encryption, it’s safe and nice
Keeping 53 opened is not that bad, the only thing you will notice is an increased load on your server if somebody tried to ddos somebody’s server using your dns
P.S. Or as somebody mentioned below, use rate limiting. It’s described pretty well in some other comments. Not just “spooky internet port”