https://www.bbc.com/news/articles/c1k81lj8nvpo
According to Ofcom, platforms must not host, share or permit content encouraging use of VPNs to get around age checks.
The government told the BBC under the Online Safety Act, it will be illegal for platforms to do this.
Ofcom is the regulator so I’m guessing they read the law a little more closely than you. And BBC states that the government explicitly told them it would be illegal.