I've got a 2017 with LED headlights and was looking to upgrade the highbeam. I had the same issue as you, i couldn't access the back of the headlamp assembly.
I was told by one of the sales guys at AutoPro earlier this week that he's come across a few cars where if it's LED from the factory, you can't open it up. Its a sealed unit. I need to ring Toyota just to confirm but it sure looks that way.
I haven't checked to see where in the wiring harness you can plug into to fit spoties or a light bar. Thats my next on my list.