Using 1,454,942 maximum size and minimum error correction QR codes in alphanumeric mode (byte mode is a lie) to store Base64-encoded binary data, you get roughly 4,687,823,124 bytes. 4.6 GB. If the cards are two-sided we get 9.2 GB.
Minimum size of Windows 11 installer image seems to be 8 GB, so it checks out!
Why Base64? QR codes can contain pure binary data, no need to use this inefficient, not-error-correcting 6-to-8 encoding.
Oh, I forgot Microsoft does not care jack shit about saving people's computing resources. However, Windows 9x installers on floppies used custom formatting except the first bootable one, allowing them to fit nearly 2 MB of useful data per floppy.
They can contain binary data, but less of it. Not sure of the details, but you get 3k bytes if binary data or 4.2k alphanumeric letters. So no big difference all in all, which is a bit silly.
Also, many QR scanners can't handle binary data and freak out on null values or newlines.
We must consider the practical side of installing Windows 11 from a semitrailer load of cardboard.
Optar is the first time I've seen someone seriously present their project as compatible (even claiming that is possibly the optimal use case) with IP over avian carriers. Craziness, but well done.
Though if they were double sided, there is no way we can see all these cards in the same shot. If it starts at odd numbers (i.e. #1), #3 and #4 would share the same card front and back, if it starts even (i.e. a cover graphic and #1 on the same card), #4 and #5 should share the same card front and back.