I've just run into this 'regression' since upgrading on my iPhone. This will be a show stopper for those relying on PPTP and needing to access corporate LANs via VPN while tethered. I need PPTP VPN access for network management purposes.

Mentioned here

https://support.apple.com/en-us/HT206844

I'll be sending feedback to Apple, but won't be holding my breath... :/