These ISP level “security filters” have been a thing in Turkey since 2011. They are optional but they always try to trick people into enabling them. There’s even safe internet day(5th February), they send you an SMS with a link to instantly enable filters to celebrate internet safety day.
What I find weird though, not all sites are blocked equally. Some are on DNS level and simply using something like Google DNS removes the blocking, others are blocked on IP level and only VPN can help. There’s no consistency between the ISP on site blocking methods.