Unable to manually parse the HEVC video with alpha format

I wish to parse the bitstream of HEVC video with alpha (specific video format reference WWDC2019: https://developer.apple.com/videos/play/wwdc2019/506).

Taking the 'puppets_with_alpha_hevc.mov' file from 'Using HEVC Video with Alpha' as an example, I would first extract the HEVC bitstream, then parse its fields. When it comes to the VPS field, as I reach the vps_extension, I find that the bitstream in 'puppets_with_alpha_hevc.mov' does not conform to the HEVC standard document, preventing further parsing.

Besides the 'HEVC Video with Alpha Interoperability Profile.pdf', are there any more detailed documents describing the HEVC video with alpha format? Also, is there anyone who can encode or decode HEVC with alpha videos on systems other than macOS?