Basically I forgot it exist and I didn't know it helps your reach. And I also didn't know that it was for disabled people. I met one person who has their phone reading them things on screen but I thought that for art it used some sort of google lens to tell what's on picture

I highly doubt google lens is that capable and that reliable. Screen readers will read out alt text, though. And yes, plenty of people (including me) will not repost images that don't have alt text (or where the poster didn't ask for alt4me). So that will limit your reach.