Throttling means cutting back on the frequency (clocks) in order to reduce the amount of generated heat. It happens when a chip (CPU or GPU) is not being cooled properly and it starts getting too hot. This is the chip's first line of defense to keep from cooking itself to death. If the temps continue to rise, it will shut itself off to prevent permanent damage.

As for your situation. You do seem to have some sort of bottleneck, since neither the CPU nor GPU are being fully utilized, but it's unclear from what you've provided what the problem is. First, the CPU usage is reported as a percentage of the threads being utilized. Not every application, particular games, can take full advantage of all the threads available. For example, if a game is only optimized to utilize four cores and eight threads, and you have an 8 core/16 thread CPU, the reported utilization may max out at around 50%, but as far as the game is concerned it's at 100% utilization. Your bottleneck in that scenario is the single core performance of the CPU, which is setting a hard limit on how much each of those threads the game is actually using can actually do.

GPU utilization is a little more straightforward, as graphics workloads are distributed by nature, but you can still have bottlenecks there such as power limits or using features that are not as heavily distributed, such as ray tracing, or exceeding your VRAM such that the GPU can't bring all the resources it has to bear at one time.

Check that your temps are not too high. For your CPU, that's anything approaching 100C, though you ideally want to see a lot lower than that, and on the GPU, approaching 85C. If you are nearing those marks, throttling could be a factor. You can also try shifting more of the workload to the GPU by using a higher resolution, higher quality settings, etc. If you can't get it budge above 70% still with a harder workload, there's likely something going on with the power limits, from maybe an underpowered PSU, or some other power delivery issue. Also check your RAM. Make sure you are actually running dual channel, for one. Using only a single stick of RAM or having a dead stick and not realizing it can severely degrade your CPU's performance.