Ah! Now I think I understand what you're trying to do. And don't think you can do it with just an Automation. Might need to use Focus.
Setup a dummy Focus, "Temp Silent". "Silence Notifications From" checked for People, no people listed. Apps, will need figure out if allow or not and what to put in the list.
Now you setup Automations, "When Focus Temp Silent Turned On" and "...Turns Off", calling appropriate flavor of silence. To activate, turn on the Focus with "until I leave".
I'm a big user of this, have several Focuses defined for different levels of silence, most have locations defined but will use on an ad-hoc basis by manually turning on per above.
Here's for leaving the theatre. Shortcuts is still cryptic enough to make one would think that this is activating Silent Mode, but clicking on the right arrow is "Turn Silent Mode Off"
This makes it confusing for me, hence my comment about tapping On/Off/Ask. I'm working under the assumption you have a Shortcut defined and that is the action and values: Turn Silent Mode Off", which is what you want for leaving the theater.
This is the Turn Silent Mode action for Watch being used, correct? If so, can tap on the Action's "Turn" and change it to "Toggle". That way can have one Shortcut to do it all, but there is no way that I know of to setup a temporary location based Automation/trigger to do a "...when leaving".