My experience is that it does not work. I suspect only with a non-battery micro, phantom power, (but I'm still testing). I have attached a battery micro and only had noise.

I also use the Ulanzi products: https://www.ulanzi.com/ You can hide everything in and around the case.

I bought this part unfortunately, it's useless because I can't mount the GoPro on my gimbal properly anymore, the cable always gets in the way.

Yes you can. However, there is no suitable housing for it because the Hero8 is larger than all other GPs.
I recommend the Media Mod https://www.digitec.ch/de/s1/product/gopro-media-mod-gehaeuse-actionkamera-zubehoer-12300574. Then you also have a clean solution without cables hanging around.