Okay so the issue is 100% the usbmount package Raspbian Buster provides. The final comment from this solution that builds the package from the git works for me. From a fresh install of Raspbian Buster this is my process.
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install git
sudo apt-get install debhelper
sudo apt-get install exfat-fuse
cd /var/tmp
git clone https://github.com/rbrito/usbmount.git
cd usbmount
sudo dpkg-buildpackage -us -uc -b
cd ..
sudo apt install ./usbmount_0.0.24_all.deb
change /etc/usbmount.conf file systems to FILESYSTEMS="vfat ext2 ext3 ext4 ntfs-3g ntfs exfat hfsplus fuseblk"
sudo reboot now
This worked for me with exfat and the drive gets mounted to /media/usb0 or /media/usb1. No extra settings or files required. Hope that works for you.
James