I thought i recalled in the past when i was using a VPN it was stopping my friends from accessing my server. Can I use a VPN and people still have access?
depends on various things.
are you putting your plex server behind a VPN? if you are then most certainly that could cause issues with people trying to connect. you are changing the WAN IP of your plex service, routing it thru a VPN, and that VPN provider might block port access that plex needs.
not sure why you would want to do that, make zero sense.