How do you set up Razer core chroma with Macbook pro 2019 and radeon rx 6900 xt?

First, make sure that the GPU is plugged in to power and seated correctly in the slot.

The first website I opened in a google search said that the 6900XT in question recommends using a 700 watt power supply. The Razer Chroma does say it is 700 Watt, but remember 50watts may be required by the USB ports and 100 is to support MacBook charging. The vanilla Razer X serves up 650Watts without the USB ports.

You are probably OK, but check with the GPU supplier and with Razer (Razer have a list somewhere on their site) for power supply compatibility for your model before wondering if you have a GPU hardware issue. I have 2 Razer X boxes on 2 different systems which I use for such issues. Do you have a way to independently check your GPU - perhaps a 'good' friend has a gaming machine you could try it out on, for example.

When the hardware issues are discounted, then we have software config, but an 6900XT should work out of the box, according to Apple (gpu drivers are built in). I have never seen a GPU fail to work plug and play (I've tried 4 different GPU's and every macOS since Catalina, except the new Sonoma - I'm working up the courage to try it).

Probably a good choice as Apple will probably stop supporting Intel Macs during the lifetime of your rig.

BTW, one of my rigs is a 14" magnesium alloy windows11 laptop (13gen i7 / 2TBSSD / 32Gb RAM - cost <1.2K) with no dedicated GPU beyond the Intel onboard stuff using an 6800XT in a Razer eGPU. It is a Beast of a system at 2K screen resolution if you are happy maxing out with the 6800.

Also, not all Thunderbolt cables are created equal. Best to use the original Razer cable, if you have it...