FYI, for others that come across this thread, you may use the command below to install the necessary WiFi drivers on your Raspberry Pi:
sudo apt-get --yes install firmware-brcm80211 && sudo reboot
Then to connect it to WiFi:
sudo nmcli device wifi connect <your-ssid> password <your-password>
Note: This is experimental. We haven’t extensively tested these drivers on the Raspberry Pi yet. Also, the WiFi configuration will be removed on the next software update. Official support for WiFi is coming in umbrelOS 1.1.