Every EPUB the studio builds is made to be read with a screen reader, a braille display or large type: headings in order, a table of contents to tap, the text in reading order, each passage in another language marked as such, and pictures with their text descriptions. Its accessibility metadata tells stores and reading apps what it offers: how it can be read, its navigation, whether every picture is described, that nothing in it flashes, and a short summary.
Pictures: a picture without a text description can't be read by someone who can't see it. Add the descriptions in your manuscript, or in the editor; the summary says when some are missing.
The EU accessibility act: from June 2025, ebooks sold in the EU must meet its accessibility requirements, but a microenterprise is exempt: a business of fewer than 10 people with a turnover, or a balance sheet, of no more than €2 million a year (Directive (EU) 2019/882). If your business is one, you can say so under Settings, Ebook accessibility. Your EPUBs then state the exemption in their metadata, as the W3C's note for it shows, with no claim of meeting the accessibility standard. They stay as accessible as before: the exemption is about what you have to promise, not what the studio builds.
Whether the exemption is yours to claim is for you to judge (the studio can't check it); if you're unsure, get legal advice. Ebooks built before you change the setting are marked out of date, so build them again before you upload them.