Had my Brennan a week or so now. I was a little bemused how to format a disk in FAT32 on my iMac. Disk Utility only shows the options of "FAT" or "exFAT".
I formatted a USB SSD in exFAT and tried to copy my music library over, but it wasn't recognised by my new B2. I formatted the drive on the B2, took it back to my iMac, copied the files to the USB SSD and then imported them onto the B2.
I then found a few tracks with missing artwork, incorrect titles and the like so wanted to copy those too. I thought I'd use a memory stick for that so I could keep the USB SSD as a "backup" in case disaster struck.
I read a few online posts and it was suggested that Apple's "Disk Utility" can format disks in FAT32. If you open Disk Utility, select the memory stick, click erase and then set the Format to "MS-DOS FAT" and the scheme to "Master Boot Record" (having set the name to something sensible too) and then click "Erase" the disk will be formatted by macOS. Once this is complete the disk should be fully readable by the Brennan. It seems as though for Apple, "FAT" actually means "FAT32", or at the least, FAT32 compatible.
I used a disk formatted in this way completely successfully with my B2 and imported a few Gb of data using it.