What's the best way to backup the OSs in VMware Workstation?
The first method is to copy the virtual machine to an external hard drive.
But of course, this isn't the best method for big enterprises, as it can consume a lot of time, and to keep your data safe, you should always follow 3-2-1 backup rule, which states that you must have 3 copies of your data on two different media (disk, tape, etc) with one copy stored offsite.
A good way to back up live VMware VMs and all application data safely is using third-party software. There are various options, like Nakivo Backup & Replication, Storware or Gheto.sh.
I like the this one https://www.nakivo.com/vmware-backup/, it's easy implement and to use, and offers image-based backups, incremental and application-aware backups, and long-term backup archival.