DSM 7.3.2 has built-in exFAT support;  no longer a separate app.
Plug in, then format the drive as EXFAT, for use on Windows or Mac. YouTube
Hyper Backup supports incremental backup and is by far most resilient; USB copy is simple.
YouTube DSM backup alternatives discussion Every home user should use it; restore could take a couple of days...
name the external USB drive (control panel > shared folder) before creating the backup task
also, Edit - hide this shared folder