you say "Group"
You can Group track in the Mixer & at side of Timeline by holding down CTRL and clicking on background of tracks you want grouped (the grouped tracks control section becomes light-blue colour instead of boring grey); then anything you do or change occurs for same control in each track. These groups remain until you click on a single track background or create another group, and I think you can only have one group active at a time..
You can also create many audio Buses in Mixer, and, if you re-route(change Output) tracks to these, they can be separately Muted or Soloed, or have common FX & Automation - additionally these Busses can be grouped as above.
Grouping 'events' is different. That will not mute or solo those in a particular group.
The sub-master mute and solo 'buttons' (icons) are identical to those on the tracks.
Unfortunately there is no function to Mute the Grouped Tracks, which I find quite bizarre. Hopefully in a futurre version the function will be implemented as real 'Folder Tracks" as has been in Acid for several versions, with full track-header and timeline functions for the 'Group'.
As it is, the only benefit is saving screen real-estate, and layout organisation.
Actually, if you have several tracks selected, clicking any mute or solo button toggles all of the tracks. Seems like that should be sufficient for a "group mute".
After creating a track group clicking on the right of the group header selects all the tracks in the group which make muting the group a little easier.
I do agree with Goeff that a group mute and solo would be nice to see in the future.