"Alt text should be as long or short as it needs to be, just succinct and correct. Alt text is not about length. It’s about purpose and context, describing what an image shows and why it matters. Some images only need a few words, others deserve more detail."
Happy that this gets debunked by Chris Yoong because I've seen it again in yet another "white paper" (maybe written by AI, who knows?)
https://chrisyoong.com/blog/the-100-150-or-200-characters-alt-text-rule-is-a-myth
https://chrisyoong.com/blog/the-100-150-or-200-characters-alt-text-rule-is-a-myth