I’m not sure if Ubuntu requires a wired internet connection. I’ve installed a different distro yesterday and wifi worked fine during the installation. The installer asked me to connect to network and I used the wifi. I’ve never plugged a network cable into the machine. Maybe it’s the same with Ubuntu. But sure, there are other possibilities. Offline installers and/or you can install Linux on a different machine and then swap the harddisk/ssd. Just take care not to overwrite the internal disk of your laptop. Make sure it writes to the correct disk (or unplug other ones).