You could theoretically install Windows 11 on less, but why does it ask for 64 GB for the installation of Windows 11 and refuse if it is less?
This is a very good decision by Microsoft, because many Windows Ultra-Books, Tablets, Mini-PCs, ... etc. were equipped with 32 GB hard drives in Windows 10, which meant that they were almost unusable after the second to third auto update and the Windows licenses are time-bound, at some point you could no longer install and the Windows could only be reloaded here by an expert!
With 64 gigabytes it is not enough, but at least it can be sufficient in the office area, but there will be insufficient space in 2 to 4 years, because the APPs and applications are exploding in terms of memory requirements. Storage space optimization is now a foreign word. So if you want to be absolutely sure you should definitely plan 128 GB or more for the Windows 11 C:\ drive. Because if you are not a Windows expert, you will need one if you get the message "There is not enough memory available"!