Ok, this part is pretty cool:

Thunderbird Assist will also be available. This experimental feature, developed in collaboration with Flower AI, offers optional artificial intelligence functionalities for users who want them while also addressing privacy concerns head-on. On devices robust enough to handle AI models locally, Thunderbird Assist processes everything on the user’s own machine.

However, for users on less powerful hardware, the development team has integrated NVIDIA’s confidential computing to keep any remote processing secure. Rest assured, those who prefer to skip AI services can continue using Thunderbird without these extras.

I've been unwilling to touch cloud based AI, much less expose my emails to it as there's no guarantee of privacy, but being able to run a local model allows you the functionality without the risk. Haven't used Thunderbird in years, but this is tempting me to give it another shot.