In the real world, your nationality doesn't prevent you from entering a casino. The same logic should apply in the virtual world—using a VPN, by itself, does not give any unfair advantage to the player.
In many countries, including mine, there are severe restrictions on access to the open internet. VPNs are a necessity just to connect to the outside world. In other regions, online poker itself is restricted or banned, and a VPN becomes essential to even access the platforms.
When it comes to multi-accounting, there are dozens of simpler and more undetectable ways to cheat than just using a VPN. Poker sites are still unable to fully detect those methods. I've said many times that the only real way to make a poker site truly fair is to verify each player's identity before they start playing. So far, only one site I know of actually enforces this.
Regarding what our friend magnus2022 suggested—asking the site directly—the unfortunate reality is that most sites won’t tell you the truth. They’ll clearly state that VPN usage is not allowed, while secretly allowing it through their affiliate agents. Even VangPoker publicly deny VPN usage but allow it silently through agents. The only major site that openly allows VPNs is CoinPoker.
As for the rest of the networks, it’s an open secret that almost all of them quietly permit VPN use, as long as it’s done through intermediaries.