I have found that by removing the clamp and end buffer rubber pieces, and adjusting the slider to its limit, my iPhone 12 Pro Max fits into the holder and is not far off being balanced.  This is with a very slim case fitted.  I've run it for a while now and all seems well.  I was ready to sell this OSMO 2 and replace it with a later model but it seems this phone isn't yet approved for any of the later models so I thought I'd try this, lucky I did!

I have found that by removing the clamp and end buffer rubber pieces, and adjusting the slider to its limit, my iPhone 12 Pro Max fits into the holder and is not far off being balanced.  This is with a very slim case fitted.  I've run it for a while now and all seems well.  I was ready to sell this OSMO 2 and replace it with a later model but it seems this phone isn't yet approved for any of the later models so I thought I'd try this, lucky I did!