Alt text gets the attention because it has a field. The rest of accessibility on social has no field, so it depends entirely on habit.
Emoji in the middle of a sentence
A screen reader says the name of every emoji out loud. Three of them between words turns a sentence into a list of descriptions. At the end of a line they are fine; scattered through the text they are not.
Hashtags in camel case
#SocialMediaTips is read as three words. #socialmediatips is read as one long noise. Capitalising each word costs nothing and works for everybody.
Contrast, and text on images
Pale grey on white looks refined on a good screen in a dark room, and disappears outdoors on a cracked phone — which is where most people are. Text baked into an image is also invisible to search and to screen readers unless the alt text repeats it.
Flashing
Fast strobing cuts can trigger seizures. It is rare, it is serious, and it is entirely avoidable — if an effect flickers more than about three times a second, it does not go out.
Captions on video
Both an accessibility measure and the thing that makes a muted video legible to everyone else. The two arguments point the same way, which is the easiest kind of decision.