Alt text
Two arguing children, representing Republicans and Democrats, each tout their support for Oligarchy or Corpocracy respectively. A third child, representing Libertarians, suggests “why don’t we have both?”
It's a very old web standard, and choice of client is frankly a matter of will, not a limitation of capacity. Capable clients exist, especially lemmy interfaces (that have supported setting it over 2 years ago) readily accessible to anyone from the web browser by navigating to their instance. Deficient clients shouldn't guide content authoring practices anymore than Internet Explorer 4 should. If anything, client deficiencies should motivate rejection of deficient clients.
Moreover, spoiler (ie, the details & summary HTML element combination) is a newer feature with less mature accessibility (though still pretty mature) than alt text, though it's pretty good for a more structured text alternative.
I'd suggest complaining to the client developer to pressure compliance and choosing a better client. Deficient clients also perpetuate structural inequity.
@cannedtuna@lemmy.world your downvote is not a valid argument whereas this comment is, and it reinforces the earlier point that the toxic culture at lemmy can't stand valid criticism of deficient choices entirely within their control to the detriment of their own community & the wider public.