Cpu at 100% while gpu at 0%

It helps if you know what the different hardware bits are used for within Premiere. And that 'hardware' and 'software' acceleration actually refer to two, completely different, processes.

The CPU is the main processing unit used. The GPU is an assistant for specific purposes. They are not 'co-equal' at all. The math in each is completely different, so you have to code specifically for CPU or GPU processing.

The GPU in Premiere is used for those things on the GPU Accelerated Effects List ... mostly things that involve resizing and/or color work. Such as Warp Stabilizer, Lumetri color, some others. It is not normally used much for basic decoding during playback, for instance. Unless there's GPU accelerated stuff going on, and the GPU will be used for those things, as the CPU calls for processing on specific things from the GPU.

The two types of 'hardware' and 'software' acceleration are the above-mentioned GPU acclerated (coded) effects for one. The other is long-GOP decoding/encoding which only refers to the use of specially designed chips in your system built for H.264/5 work.

And for that second terminology usage, this depends on whether your computer has the right chips in it for that process. Many don't, some do. In your Preferences, one of the tabs has a pair of options to enable hardware processing of H.264 and H.265 encoding and decoding.

So if you are doing an mp4 export, for instance, a long-GOP codec, you will see in the Export dialog summary a statement for either 'hardware encoding' or 'software encoding' ... and the Export dialog summary NEVER refers to whether or not your export will involve the GPU. ONLY whether or not you have 1) the proper chips in your computer and 2) the option to use them turned on.

If both are 'true', then you get 'hardware encoding' in the Export dialog summary. If either is not true, you get the phrase 'software encoding' there ... and again, this has nothing whatever to do with your GPU.

If in your Project settings dialog, you have the option for Mercury Acceleration, typically CUDA (Nvidia GPUs) or Metal (AMD GPUs on Macs). If you can set an option there, then your GPU will be used for those things which a GPU is used for in Premiere, and as the CPU sends data to the GPU.

I hope that fills in some details for you.

Neil