Anyone else seeing the problem in Calendar where you can't use 24 hour time when creating an appointment even though everything on system is set to 24 hour time. Once it is created it shows as 24 hour time but only has am/pm option for creation editing. This is specific to iOS, not a problem with iPadOS, or with Big Sur. Still there in Beta 5.
See screenshot - note it shows start time in 24 hour format but editing is only using am/pm.
See screenshot - note it shows start time in 24 hour format but editing is only using am/pm.