

If you’re saying you started on Gnome, then dropped in another DE, you need to switch to an agnostic network manager if you were relying on Gnome’s Desktop Network manager implementation probably.
If you’re saying you booted a clean Fedora Cosmic LiveUSB and couldn’t get WiFi working, you need to look at logs or run through some cli debugging to see what’s up. Probably just Cosmic issues.
Edit: forgot about nmtui. You can use this to debug issues from the clinpretty simply if the desktop tools are failing.
Try using your CMOS’ EFI boot manager and see if it sees both. If so, just skip Grub and use that.