Upgrading FreePBX to newer Asterisk version

I’ve upgraded an non-production FreePBX installation which was running Asterisk 15. I’ve used the upgrade script (after a full backup of the virtual machine) that was available for asterisk and it seems to work fine but it did not answer my question if there is a relation between an up-to-date FreePBX installation and an Asterisk version (eg 16, 18, 20).

Is there any limitation in this matter ?

You can easly use an up-to-date FreePBX installation with an EOL Asterisk version. You can get current by running ‘asterisk-version-switch’ script from the CLI and get to an Asterisk LTS version in less than 5 minutes.

I’d run at least asterisk 16. You can switch on the fly Changing Major Asterisk Versions on the Fly - PBX Platforms - Documentation