alt Hacker NewsStandard link to download: https://dokumen.pub/download/hdmi-specification-21-high-defi...
Alternative: https://annas-archive.org/md5/4dd395c749519a36cb755e6ebbe488...
Alternative (incomplete, only couple first page): https://device.report/m/91235972e8cbf6d6ce84f7cf84ca0ac12623...
Other HDMI stuff: https://pdfhost.io/v/YidEvBDkS_EP92A7E_EP91A7E_DS_V04
Older available here: https://glenwing.github.io/docs/
AIUI the spec being leaked ironically makes things worse, because for an unofficial implementation to be legally kosher it would have to be clean-room reverse engineered anyway, and since the official spec is out there the integrity of such an effort would be called into doubt. You'd somehow have to prove you didn't look at it, ever, or at least be trusted enough for people to take your word for it.
(I'm not a lawyer, please correct me if I'm wrong)