Thanks all - this worked great over here as well on a macOS Big Sur and LG BU40N with factory 1.04 model. I first flashed to 1.04MK (using the ‘enc’ option) and then to 1.03MK (without ‘enc’ option) and seems good so far.
I also took a gamble on a cheap £9 case off Amazon having been inspired by a previous poster using one from aliexpress. It worked just fine. The one I used was this 9.5mm EHZ-SHOP model: https://www.amazon.co.uk/gp/product/B077D2HS6W
The place to discuss Mac OS X version of MakeMKV