Big screen beyond came out in '23. Meta has made strides with their recent showings. And I don't believe anybody is really dumping vast sums of money into it quite yet, they're coasting somewhat (though I realise that that's conjecture).

I'd say the biggest unsolved issue is the focus/depth of field issue...how to provide variable per pixel depth so that virtual objects can appear in a scene and be focussed on naturally (apparently called vergence–accommodation conflict) since most if not all displays have a fixed focus distance atm.