You can download a “backup” of your config through the GUI (at least under “Advanced” or “LuCI”) or from the command line. It is a tar file that can be expanded and viewed on most desktops.

Within the same major release from the same sources, you should be safe to keep your settings.

If you are, for example, upgrading from GL.iNet v2 to GL.iNet v3, across GL.iNet and OpenWrt, from OpenWrt v17 to v18 or v19, or from ar71xx to ath79, or downgrading in any way, then reconstructing your config is the approach I’d recommended.