There have been a couple of these cases already, and so far they've lost. Because they charge, the T/P/M restrictions you put on these can be more restrictive than say if you were trying to ban a free indoor Trump or BLM rally or a free religious service. One of the reasons, though, they've lost is that generally they've been held to a similar standard as indoor dining and other indoor facilities....where it gets tricky is when they are treated differently. So far, in most places if the indoor restaurants have been shut so have the theaters. See also the poll dancer cases in San Diego and Buffalo.
The bigger vulnerability for lockdowns is the lack of a rational basis behind certain governmental policies (outdoor dining, and maybe even schools). Given the data that's emerged, the behavior of some officials (like Newsom and the LA Supervisor), and public statements by California, HHS, and La County that they don't have data showing outdoor dining---> spread, it's an area of vulnerability. Leaves them only the argument it was a necessary step to stop people from gathering (but they'd have to prove that's the case....don't know if they can). Gorsuch's concurrence touched on this and I think he was signaling to folks his concern about this issue (Alito too given his remarks on lockdown, but he's approaching it more from an executive action without legislative input for too long approach)