I usually remove the work box and just do a bracket / "mud ring" / whatever you want to call it, like this: https://www.amazon.com/Single-Drywall-Bracket-Voltage-Mounting/dp/B08KPPP2R6
The tech will carry those, we use them all the time.
And a side question, are you doing internet only or TV as well? Just curious because if you're internet only you won't be needing coax regardless, it would be ethernet from the ONT to the router.