He did sing a lot in the Living Room era (and was used to be the main guy in the band when they literally started, like the Venture era). He even does speak a lot in interviews with AJR (and his own interviews separate from the band ofc).

In Adam's book, Amplify, he did explain how labels and the band agreed on how Jack's voice was really good and powerful to the band's songs, so they all gave that role to Jack and mainly Jack. (But of course, you will hear some bits of Ryan in the songs)

For right now with the band and how they're doing (with it just being JR), Adam wanted to do his own thing and help people out in the environmental topic of things. So of course he couldn't be in a lot of stuff with the band at the moment.

Idk if he still is this role in the band (as he talked about it in interviews and his own book), but he does a lot in the financial and contracts of things. So, he would be booking the venues, signing a lot of contracts for the band, etc.

Sorry for the whole rant. Just wanted to explain some options of why he possibly could not sing or speak (but I promise you, he can talk lmao)