I had (and lost, unforunately) a pair of Sennheiser MM400 headphones... The charging jack was on the removable battery pack and you could charge it while using it (no effect at all on headphone operation)

> All headphones and earphones I’ve tried will cut off everything else while they are being charged. Including Bose and Apple.

This has not been my experience with my AirPods Max. They work over Bluetooth just fine while being charged, unless they are completely depleted (0% battery).

For reference, this is on firmware version 4A400 but this has been the case since I received them (months ago).

I’ve used my B&W PX over Bluetooth while charging over USB-C.

They also support playback input over USB-C or 3.5mm. It’s nice. Expensive, though. But not Apple Airpods Max expensive, at least!

I also have the B&W PX and can confirm this.

I don't love these headphones though. They clamp on my head way too hard for extended use.

Turtle Beach can charge while using. And play two inputs at once. The biggest downsides are how ugly they look and lack of NC.

Adding another one, my Sennheiser PXC 550 (both original and II) will charge and do bluetooth or wired audio.

I bought a used set of Bose QC (Quiet Comfort) and they came with two removable batteries and a charger, all packed nicely in a really small case.

I replaced the foam for $7 at some point but they still worked nicely last time I checked despite being 7 or so years old now.

Weird, I can charge and listen to my Sennheiser Momentus Wireless 3 at the same time.

Jabra 85h can charge over USB C and play over Bluetooth at the same time.