Not so much an expert rather than just parroting what I saw, but according to a cursory search, and a Twitter community note I saw from a friend, the voice used by this project is Synthesizer V, which is actually a perfectly legitimate piece of software for using digital voices in music production. If you've heard of Vocaloid, or know about Hatsune Miku, SynthV is basically a competitor in that space.
Going back to the community note, the voice used is actually called Natalie, and apparently the TOS of SynthV does not allow use of its voices using a name that's different to what was given. So they essentially can't present the Natalie voice as Anna, which they are.
EDIT: I want to clarify that these voice synthesisers like SynthV and Vocaloid are usually based on the recording of someone who has consented to the use of their voice in that regard and has been paid for it. It's not like the current AI voice cloning trend going on.
No prob! These digital voices have been around for over a decade now, maybe more. Some of them use "AI" to improve the sound of the voice (i.e. support more languages than actually recorded, make it sound realistic) but not in the way that current AI voice trends are going.