[kelnos]

with everyone connecting from home, what percentage are behind a LAN firewall

From home? Essentially 100%.

that you need to use TURN servers?

That's less clear. I'm not sure how many home firewalls are impenetrable by STUN as well. I worked on Twilio's WebRTC-based audio product back in 2012-2014. In the beginning we only supported STUN. We did get some customer support requests about initial connection failures (which I mostly attributed to STUN failures), but never kept track of stats on what the success/fail ratio was. We eventually added TURN support (after I left that product team), but based on how long it took us to do that, my guess would be STUN was effective for most setups. Also consider that many (most?) of our users were probably behind restrictive corporate firewalls, and I'd expect home firewalls to be more lenient.