How does Google know you're on a VPN? I'd assume that it could only be inferred from the source IP address of your UA, which implies Google keeps track of well-known VPN source IPs. However, apart from the fact this is imperfect (I assume IP blocks are shifting all the time?) you could easily spin up a VPN of your own on a cloud VPS, in which case tracking IP blocks wouldn't work.
Perhaps simplest of all, you could always sign up for the email on a semi/public wifi access point, or even from a shared computer, as from an internet cafe or even a friends phone.
VPN detection isn’t rocket science. It’s a commodity and works well for Netflix and all other services relying on geo ip detection. It’s not always accurate but works well enough. Blocking data center IP ranges is also done frequently and so spinning up a VPS on a provider like DigitalOcean won’t work.
The most likely option to use is residential proxies which are real IPs of devices, these are very hard to block but expensive.
Probably best to just go to a public wifi and used a burner phone if that’s what you want to do.
Cloud VPSs can be looked up and you can see theyre a datacenter IP, which is probably assumed to be "VPN" by default. I'm running my own vpn like that, but i still get blocked on sites for use of a VPN.
Perhaps simplest of all, you could always sign up for the email on a semi/public wifi access point, or even from a shared computer, as from an internet cafe or even a friends phone.