Install Windows 10 on your Mac with Boot Camp Assistant - Apple Support recommends 64GB as minimum required. I recommend 256GB-384GB. From the link...
- When Boot Camp Assistant asks you to set the size of the Windows partition, remember the minimum storage-space requirements in the previous section. Set a partition size that meets your needs, because you can't change its size later.
If you need to enlarge the partition later, you will need to remove and re-install Windows.
This is from a 2018 Mini.
diskutil list
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk0
1: EFI EFI 314.6 MB disk0s1
2: Apple_APFS Container disk1 616.0 GB disk0s2
3: Microsoft Basic Data BOOTCAMP 384.2 GB disk0s3