I’ve noticed a large conversation around getting "Support for Apple Music with Google Assistant”, whereby people were frustrated that Google Assistant on Sonos doesn’t support the ability to play music from Apple Music at this time. I just wanted to make people aware that they can workaround this limitation, albeit in a very limited capacity, by using IFTTT to play a specific "Sonos Favourite" you’ve already “Added to your My Sonos” app home screen area.
Requirements: You’ll need to first have a basic IFTTT account with Google Assistant and Sonos added as Services. And you’ll need to have already added what you want Google Assistant to specifically play (ie a playlist) to your My Sonos area by selecting it in the Sonos app and choosing the option "Add Playlist to My Sonos".
Steps: You then “create” a new applet in IFTTT that uses Google Assistant service for the "If This" part choosing "Say a simple phrase” to trigger it. Then you choose the "Then That” action which uses the Sonos service to activate the trigger by choosing to “Play Favourite” (which should display the items you’ve already added to My Sonos in a drop down list).
Troubleshooting: If you already have an IFTTT account with Sonos added as a service that you haven’t used in a while, you may need to reconnect Sonos as a service. The simply phrase used as a Google Assistant trigger can’t use the keyword "play", so use “listen” instead (ie “listen to the Best of the 1970s"). Note that Google Assistant is not actually processing the words in the simply phrase you use as a trigger, it’s just listening for the phrase as a whole and activating an action based on it. So you could use and say the phrase “Howdy Doody” to play a playlist of your favourite R&B music you’ve already added to My Sonos if you wanted to. BTW you can also have Google Assistant say something specific in response to your trigger phrase (ie Ok, listening to your Best of the 1970s playlist), otherwise it will just say "performing action”. Finally note that the Free plan of IFTTT only lets you create 5 applet actions (so just five custom phrases to play different My Sonos favorites).