I tested the Chromecast app for Homey, and it works great with my Google Home(s), but I can only set a volume percentage, not increase/decrease volume.
I’d love the possibility to control the volume relatively (increase/decrease 5%), f.ex. with the Fibaro KeyFob remote, but it doesn’t seem to be a card that does this (yet?).
It’s the only thing I hate with Google devices, when you play music the microphone can’t hear you, and doesn’t let you lower the volume without physically touching the speaker, or using the Google Home app.