idiotsecant parent
If your threat is state sponsored bad actors you've already failed. OK, great you blocked VPNs. Now they tunneled their vpn through as HTTPS. You successfully annoyed all your legit users and completely failed to stop the real problem.
Https is also inspected in our place and has been for a decade.
Also there's different classes of state sponsored APT groups. You won't stand a chance against the NSA but there's a lot of state sponsored groups in Russia that are just looking for low hanging fruit to get some foreign money for their regime.