This isn't extensive, which might be a tad misleading if you don't double check. They test on Chrome & Samsung for Android, and iOS is only the one engine.
And those three browsers seem to be the only mobile browsers that have implemented it. (Well, Opera Mobile as well). [0]
Desktop support is also extremely spotty.
This seems like it might be leaping the gun on expecting this standard to pick up the slack.
Whilst they might feel the support is there for their particular audience after 2019, I wouldn't, and would suggest that you need to check your particular audience closely before following this advice for your own site. (Which is fairly generic advice, but appropriate.)