Is there a way in MacOS to view filesystem details, including cluster size, for an already created exFAT partition?
You can use either diskutil info ... or sudo newfs_exfat -N ... to get various (but different) details of your ExFAT file system:


Get the device list:

diskutil list

Choose the partition:

diskutil info diskXsY


Example:

user@host ~ % diskutil info disk1s2
   Device Identifier:         disk1s2
   Device Node:               /dev/disk1s2
   Whole:                     No
   Part of Whole:             disk1

   Volume Name:               Share
   Mounted:                   Yes
   Mount Point:               /Volumes/Share

   Partition Type:            Microsoft Basic Data
   File System Personality:   ExFAT
   Type (Bundle):             exfat
   Name (User Visible):       ExFAT

   OS Can Be Installed:       No
   Media Type:                Generic
   Protocol:                  PCI
   SMART Status:              Not Supported
   Volume UUID:               B44618D6-7DA7-35B0-BB27-C39785AA75F8
   Disk / Partition UUID:     7C734251-4E83-4537-885C-237D94F50633
   Partition Offset:          210763776 Bytes (411648 512-Byte-Device-Blocks)

   Disk Size:                 1.1 TB (1073530011648 Bytes) (exactly 2096738304 512-Byte-Units)
   Device Block Size:         512 Bytes

   Volume Total Space:        1.1 TB (1073495408640 Bytes) (exactly 2096670720 512-Byte-Units)
   Volume Used Space:         10.0 MB (9961472 Bytes) (exactly 19456 512-Byte-Units) (0.0%)
   Volume Free Space:         1.1 TB (1073485447168 Bytes) (exactly 2096651264 512-Byte-Units) (100.0%)
   Allocation Block Size:     131072 Bytes

   Read-Only Media:           No
   Read-Only Volume:          No

   Device Location:           Internal
   Removable Media:           Fixed

   Solid State:               Yes
   Hardware AES Support:      No

or sudo newfs_exfat -N diskXsY

Example:

user@host ~ % sudo newfs_exfat -N disk1s2
Reformatting existing ExFAT volume
Partition offset : 411648 sectors (210763776 bytes)
Volume size      : 2096738304 sectors (1073530011648 bytes)
Bytes per sector : 512
Bytes per cluster: 131072
FAT offset       : 2048 sectors (1048576 bytes)
# FAT sectors    : 65536
Number of FATs   : 1
Cluster offset   : 67584 sectors (34603008 bytes)
# Clusters       : 8190120
Volume Serial #  : 5ea31cc5
Bitmap start     : 2
Bitmap file size : 1023765
Upcase start     : 10
Upcase file size : 5836
Root start       : 11


Hint: the message "Reformatting existing ExFAT volume" is misleading; the file system won't be altered.
   From man newfs_exfat:  

-N      Don't create a file system: just print out parameters.