alt text inside illustrator for accessibility

I did the ff steps but didn't work.

I grouped the layers as one > sliced it, inside the slice option I was able to accessed the alt text dialog box and then added the alt text.

I have to submit the file in jpg but when I tested it for accessibility as jpg. I can't see the alt text when hovering and screen reader is reading it as "no visible tag".

I saved file as png and i got the same thing. I wish I can just submit it as pdf then this way I can add all txt to each individual elements inside the design.