No. As much as I would like it to be the case, that is most certainly a poor criteria to evaluate a UI library.
Dear ImGui [0] is without a doubt the most prevalent immediate mode UI library. It does not have native accessibility features, but that hasn't stopped companies such as Intel, Meta, IKEA and Google from shipping products built upon it. It's also used in a ton of games.
Calling Dear ImGui a toy project at this point would be like calling Unreal Engine a toy project.
It's a shame accessibility support is not more widespread, and furthermore it's a shame that it is so laborious to add it.