A massive bug is when something is designed to work in a certain way, but it’s not doing it. The ATC unit is not a bug because I don’t think it was designed with different regions in mind.
As far as I remember, all of the Microsoft Flight Simulator series from FSX, FS2004 and earlier all use inHg unit everywhere in the world.
Request to have hPa in other regions or even using the metric altitude unit for flying in Chinese airspace, is something of a wishlist that we can suggest Asobo to make the ATC more improved and immersive. It’s not considered as a bug fix.
If you set the sim to “metric” which was a request right in the beginning you get it in metrics. Distances in km, altitudes in meters I believe, speed in km/h. Meant well, known nothing, didn’t inform themselves properly either, consequently done it wrong. As so much else. Aviation units are usually a mix and that’s what should be possible to get.
The metric/hybrid setting in the options is only meant for the UI, like when you do flight planning, and changing the aircraft fuel and payload weights. It was never designed for the ATC to use it as well. Even that was a new feature added post-release.
I thought I had gotten a QNH (metric) report instead of “altimeter” in EDDN last time… But could be it said “QNH” and then inches anyway… not sure anymore.
They always say QNH in the ATC after the last few updates, instead of “Altimeter” before that. But the units they use after they say QNH is always inHg and not hPa.