In Thailand porn was straight up illegal for ages and everything else was sane and open... until new government decided to kill freedom of speech.
So slippery slope is illusion. If government is bad it don't need to try to be so complicated and gradual. It can't even think so far ahead, they will no longer be elected when that times comes.
As for social media banning for teens that's just common sense. Social media is fuming pile of garbage designed to make people feel miserable so that corporate overlords make $$$ https://www.bbc.com/news/technology-58570353.amp
And your examples only show that where there’s no safeguards, governments don’t need to be subtle, but in semi-functional democracies, they still need to at least pretend to be electable.
it's not slippery slope when it's things that happened at different times. there are examples where x did not lead to y as well as where y happened without x happening before it.