We have taken parents rights away to allow children to make decisions on their gender and name changes, yet we expect parent to be responsible for their actions like accessing porn.
That's not a contradiction. Gender and name are about who the child is. Porn is about who the child wants to imagine having sex with. One of them, 99% of children are perfectly capable of making a good decision on. One of them can potentially be traumatising, and certainly isn't absolutely necessary for a good life and healthy development.
That said, it's not the government's job to control it. An "I am 18" button and a lesson in health class are enough.
If porn sites must be legislated, here's a better way: force them to display information to users on unrealistic depictions, the dangers of underage sex, and counselling resources.
You can block tiktok's domains at the router DNS level. At least then they can't watch it on the home wifi.