In a 30 minute video Peter Pee over on YouTube compared the iPhone 6,7,11, SE2, 12Pro & 12Mini in a somewhat standardized Trueplay method. The frequency response results are all very different, offering a different sound depending on the device used.
I am wondering if some of the newer dialog issues reported by Arc owners could be linked to the device they used during Trueplay. Some users here have reported that turning Trueplay off gives them back some midrange, vocals or brings the Arc back to life. This video could show why that is for some.
TL;DR the iPhone SE2 & 12 Mini offer the most desirable Trueplay results. The disappointing 12pro results are shown the 22:00 mark. by showing the frequency response from the Arc by itself, no sub, no surrounds. Before in the grey line, blue being the 12Pro.
What device are you using? Let me know how the tuning works out for you. I added this to home theater as this involves the Sonos Arc. Links are in bold.