Hi!
I found where I read about the support to backup and restore between versions.
From
I quote
Three of the most important features we are planning for FreePBX 15 is a complete revamp of our RestAPI, Backup and Restore upgrades, so you will - in the future - be able to restore from and to a different versions (Only 15 and higher, so will be able to restore - for example - 15 into 16 or 17 into 15), and a new File Store module, which will allow you to store backups (or faxes and other files) on S3, FTP, email, ssh and more!
That’s planned for the future and isn’t available now…
Have a nice day!
Nick