If something is so hard to implement that everyone who tries gets it wrong (to a first approximation), then maybe the concept is bad. Or, at least, the concept isn't fully baked and is missing something critical.

I'd go for an action log. It's almost the same thing, but notifications imply ephemeral pokes about some of the stuff that happened, mixed with engagement boosting spam - there's a lot of unpredictability embedded in this concept, as the app is usually trying to guess what you may (or it thinks you should) find relevant.

An action/activity log is just a reverse-chonological log of things that happened. You could make one by recording every would-be toast and putting it on that list, complete with a timestamp, and any of the context-relevant action buttons (like "undo", or "view item", etc.). The list should be a fixed recording[0], without any way to dismiss some or all of the entries. Add some attention-grabbing indicator whenever something is added there, and you get all the benefits of toasts with none of the drawbacks: the log lets you report completion of optimistically-executed actions, provide place for context-relevant buttons, and also is accessible, can be browsed at uses' own time, improves discoverability and learning, and can be upgraded to also enable undo feature.

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[0] - Well, appended from top, and possibly unwinded by undo. Users understand that. Can't be append-only, because mixing that with undo gives you the undo system from Emacs - very powerful but also nearly incomprehensible to most people.

> Browsers that support JavaScript typically implement the Notification API. This API asks for user confirmation to allow popups and give the programmer the opportunity to display notifications with a text (body) along with an descriptive icon and header.

https://en.wikipedia.org/wiki/Pop-up_notification#JavaScript

Screen reader's probably not going to catch a transient element unless you just happen to stumble across it within that narrow window. Slow reader for whatever reason? Hope you don't take too long, or hope that toast wasn't actually important/actionable for you.