Unable to get TeleGuard working in Lubuntu 22.04

I installed a Swisscows app called TeleGuard (on my copy of Lubuntu 22.04.4) the other day and when I tried to run it, I got a solid (but small) black box on the desktop and this error message...

** (teleguard_desktop:2287): WARNING **: 04:04:09.100: Failed to start Flutter renderer: No available configurations for the given RGBA pixel format

I installed Flutter and confirmed that it's set up and initialized but I still receive the same message. Does anyone know how I might resolve this and get the app working? In case it helps, here's the web link for the app...

https://teleguard.com/en

Thank you for your help! :-)