As part of my backup system/routine I regularly make a backup from within Roon of my Nucleus using a thumb drive in exFAT format over USB.
Just like eating your greens and only squeezing a toothpaste tube from the bottom, for as long as I can remember I have always formally and specifically unmounted and ejected any such device on a macOS machine.
Is deliberately ejecting necessary with Nucleus + RoonOS + exFAT, please: I can’t see how to do so.
exFAT is a simple file system and it’s less prone to corruption caused by uncleanly unmounting (at least as long as you don’t pull it while there is an active write) compared to NTFS, but it is still not a great idea to do an unclean unmount with any file system. exFAT even has a dirty bit to signal if it was uncleanly unmounted: