Wow, WHAT IS THIS! Those animations are just so impressive, it's incredible what people do nowadays with SVG animations (that's SVG animation, right?!).
It's basically an after effects vector animation for each letter of the alphabet[1], which is rendered as SVG (JSON really) with bodymovin[2], and played back (maybe with lottie?) with key bindings.
[1] https://animography.net/products/mobilo [2] https://aescripts.com/bodymovin/