In a surprise move that was greatly appreciated by me and many other mobile filmmakers, Moondog Labs released a new filter mount that covers all 3 cameras on the iPhone 11 Pro at the same time. That's huge and the first one I've seen that does this perfectly (Sandmarc has an ND filter that works too, but it can be hit or miss depending on placement since it's a clip-on).
The really great thing too is just how affordable this is ($35 USD) and how easy it is to use. It's also extremely light and thus one of the most portable filter mounts I've ever used.
Keep in mind though that this is for using the built-in lenses only. This does not work with external lenses such as the Moondog Labs anamorphic lens (there's a different filter mount for it). But today with the variety of lenses on the new iPhone I'm finding I don't use third-party lenses as much - although, I still do some and actually recommend it for low light shooting especially or for stylized looks like the aforementioned anamorphic (along with fisheye or macro depending on what you're shooting).
But this filter really surprised me with it's simple design, yet powerful results. Oh, and this will also work with single or dual camera phones. You just need a bayonet mount case such as one from Moment or RhinoShield.
You can buy the Multi-Camera Filter Mount here.
Happy fillmmaking!