FB which is where most of my peers are active. Plus useful groups/ pages. It's become less personal over time, partly life stage, fatigue and data concerns. Not helped by every update enshittifying it.
I lightly dabble with insta. Not much posting, but some people transfered more to posting on there. I follow a small number of other accounts of interest.
You tube/ shorts cover any content that I would be interested in from Tik Tok, but I prefer long form content.
Never did snapchat. I never saw a great benefit and prefer more functional messaging methods.
It's easy to diss social media, and it certainly has its pitfalls (kept the DCs off most except WA, and that with caution) but there can be a lot of good there too. I did C25k because seeing friends running made me believe it was viable. Forums made me aware of C25k in the first place. Social media has made exercise and fitness far more accessible to me than traditional media such as books and magazines ever could- that content was created by proficient runners/ participants for other proficient runners/ participants.
There's loads of random, interesting, geeky, obscure content out there that has never or at least been very lightly touched by traditional broadcasters/ media, and I've gained a huge amount from SM content in the past 20 years.