extra backup HD, using TM
1) Is it better to encrypt the HDD before using it, by re-formatting it? Should do it in the GUID map or masterboot? Or should I fill it with the files and then encrypt it all with F.Vault?
2) If I use HD APFS Encrypted for that external extra back up, will I be able to read the files in an another mac? In Systems previous to 10.15 (catalina) ?
3) Can I use the TM for that extra backup (besides the TM permanently attached to my mac) choosing not to include the "system files and apps" and then choose whatever I want to back up using the symbols (+/-) or is it better to use a non apple back-up software for this extra backup, like SyncFolders, for instance?
iMac 21.5″, macOS 10.15