Apple's code is a simple circular barcode, essentially. I worked in one such format long time ago (ShotCode) - they have some benefits like resistance to motion blur and being easy to parse in low res cameras (compared to qr codes, for instance), but can't encode a lot of data (main drawback). ShotCode's reading algo is proprietary, like Apple's, but they're rather simple to implement.

some analysis here: https://www.xeraina.ch/reports/P6_2015_Circular_Codes.pdf

There haven't been any analysis to the best of my knowledge.

I saw some Twitter threads early on with people trying to figure it out but those efforts seemed to have died out.