So, according to Jason Evangelho (Thunderbird team), when I asked for an ETA:

Currently, we’re shooting for after Thunderbird 115 releases. It could either be late Summer or very early fall. Once we get the Account Autodiscovery module from Thunderbird desktop integrated, we’ll be pretty close to flipping the switch. And we’ll be sure to keep everyone posted on our blog at https://blog.thunderbird.net

Also more info at https://blog.thunderbird.net/2022/06/faq-thunderbird-mobile-and-k-9-mail/ and https://blog.thunderbird.net/category/thunderbird-mobile/

Their road map: https://developer.thunderbird.net/planning/android-roadmap