In 2016, the Erdogan regime began blocking VPN services and Tor. Now Turkey is using deep packet inspection techniques, similar to China, to detect and block VPN and Tor traffic.
The use of a VPN connection in Turkey can also mark you out as a person of interest for law enforcement. Despite this, VPN usage in Turkey is quite widespread.
The website Turkey Blocks monitors internet censorship in Turkey.
https://protonvpn.com/blog/are-vpns-illegal/