An acquaintance was kind enough to send me a pic of the ISO dial on his new 2022 M6. He can set his to 400.
Ask them if they can set it to 160 when shooting Portra - you might have to swap cameras between the two of you depending on what film you shoot

Sorry about your problems though. It sucks if a product as expensive as this one is (1) faulty and (2) the repair/replacement process just doesn't work.
I'm afraid that qualifications like 'handmade', 'craftsmanship' etc. are not necessarily advantages in a world where industrial automation has made mass-produced and machine-made/assembled products often of extremely high and consistent quality. The era that human hands were ultimately a better way to make things is really behind us. Even 'cheap junk' from China is more in line with 6-Sigma like quality control these days than artisanally produced equipment. Humans are fallible - more so than assembly robots and CNC machines (etc.).