Microsoft historically used the 21 512 byte sector, 80 track, double-sided DMF format for 3 1/2" Windows installation media, yielding 1,720,320 bytes per floppy.
Assuming this format, floppy requirements for the four Windows 10 21H1 variants currently on MSDN are
x64 Consumer (Home/Pro): 3,398 floppies
x64 Business (Enterprise/Education): 3,323 floppies
x86 Consumer: 2,416 floppies
x86 Business: 2,361 floppies
Assuming the "1.44 MB" (18 512 byte sector, 80 track, double-sided) format, you'd need
x64 Consumer: 3,965 floppies
x64 Business: 3,876 floppies
x86 Consumer: 2,819 floppies
x86 Business: 2,755 floppies
In this case, assuming the most popular (x64) platform, you'd actually need closer to 4,000 floppies.
Assuming ideal 500 kbit/sec performance and two seconds per disk swap, reading 4,000 "1.44 MB" floppies (or DMF floppies with equivalent data) would take just under 28 1/2 hours.
So you could easily install any Windows 10 21H1 version from floppies in the course of a single work week, with enough time left over, perhaps, to check Windows Update over a 56 kbps modem (though you'd probably need the weekend, at least, to actually download the updates).
