I still have an Instagram account because that's where my friends / past friends are. I've backed up and removed all my posts, and even when I was "actively posting," I hardly used it. Now it's only for communicating with people with whom I have no other way of speaking.
I still use YouTube, and do, in fact, use YouTube Premium. I'm on a family account, and while there are decent clients that I situationally use, there is no real alternative for the platform itself due to the nature of user-generated content platforms.
I no longer use my Reddit account, but I do read threads when they come up in search engine results, and many times, I do specifically narrow my search to the Reddit domain. Too much information there to completely ignore.
My Discord account is still active, although I have successfully managed to get my best friend off of there, which was like 99.5% of my Discord usage. But unfortunately because the informational age of the internet is dying, many products and games choose to use Discord for official support, which means that information is no longer indexable and only exists in the neutron star that is Discord.
So when people ask if I use mainstream social media (I can count on one hand how many times this has been asked), my quick answer is just "YouTube."

