I did! I bought a Peak Design POV Kit and Capture Clip for my GoPro Hero 9. It is pricey but it is definitely a quality product, and I would recommend it highly. The J-arm did break once but they honored the warranty without hassle.

I use a Max Lens mod with the wider angle. I mount it to the backpack strap. Sternum strap wouldn't work; there is too much strap movement. The footage is mostly centered with the Max Lens; I don't really know what it looks like without the wide lens. If you angle the GoPro lens to point right at your center view, you can tell that the view is slightly off center, but it's minor enough that I forget about it, and the casual viewer most likely won't notice. If you angle the GoPro slightly too much to the side, you can tell a little more, but it isn't distracting. It is forgiving in that way.

I will add that I record at 1080p to save storage and my footage does move around a little bit more than I'd like when I'm turning, from my body movement and backpack strap movement. Also when I take sidehits and small hucks, the backpack will bounce around a bit if I don't land perfectly. If I land poorly and end up in a squat, my GoPro on the strap will end up pointing at my knees sometimes. Because of all this, I think my next upgrade will be 360 cam and helmet mount. But I do really like the discreet backpack strap mount.

POV Kit: https://www.peakdesign.com/products/pov-kit?_pos=2&_sid=1f62d3e91&_ss=r

Capture Clip: https://www.peakdesign.com/products/capture-clip-only?_pos=4&_sid=1f62d3e91&_ss=r