Graphics card: AMD RADEON RX 6600 either 6 or 8 GB.
CPU: Intel Core i7-10700k Comet Lake 3.8GHz.
Eight core Lga 1200 10th Gen.
I just upgraded my CPU, RAM sticks (32GB total over 4 16GB 2400 DDR4), duel heat sink fan and my GPU Card. I had task manager open to check on the Memory usage. I noticed that my CPU usage shot up to 100% while using the rendering feature and export the video file to Media Encoder to render out. When rendering my CPU is working at 100% and my GPU is working at 3% at the most. I have my rendering and playback settings set to: Mercury Playback Engine GPU accelerated OpenCl in both Premiere Pro and Media Encoder.
I even used the GPUSniffer.Exe file and the CPU is still doing all of the work rendering a video and not sharing the load with the GPU.
The GPU is not simply an assistant to the CPU ... they're different hardware, and used for different things. Plus each NLE's developers have their own ideas of how to best use resources during 'typical' user scenarios.
So ... as Peru Bob says, you probably don't have anything there that Premiere assigns to the GPU ... such as all the effects on the GPU Accelerated Effects list. Such things as color work or major resizing.
When you do hit those, the GPU will be assigned work, otherwise it may not.