Adding Photos On Fb

how do u upload a photo on someone else's thread? i thought i had done this a lot, but just now startled to find the only "add" buttons showing are "emoji" "gif" and "sticker". and even if i made the pic a gif (it's a jpg at present), i don't see any method for SELECTING the file -- it just lets u put in some buzzword and choose from some sort of online FB "gif store".

i KNOW ppl are uploading files! what's the trick? or do i just have ONE USER who has turned off this capability somehow?