Bluesky has made it easier to add alt text, but some still struggle with HOW to write alt text. Sighted users who don't rely on alt text might feel overwhelmed. They might have questions on what details to include, or how to get started. This post from Veronica Lewis is a great resource.

There are so many good threads on alt text.

This is a really straight-forward introduction.
But also, never forget, if you're posting a screenshot of text (eg a magazine or website page) that also needs alt text and many apps enable you to copy-paste the text directly.