Does anyone have any info on how they built that (libraries, techniques, even artistic style).
Not a ton of clues in the source (aside from tailwind CSS)
More broadly - any advice for trying to build a LP similar to theirs?
If there's a specific part that impresses you drill into it with devtools, just pull out the bits you like and practice till you can do it yourself.
There's plenty of 'landing pages as a service' out there too. https://zapier.com/blog/best-landing-page-builders/