Davinci Resolve heavy CPU usage

Hello,
I'm using the free version of Davinci Resolve 16.2.8 after making a new, clean windows installation.
I've just downloaded again, I'm using 4k h264 footage and I have my cache location inside my OS disk and the export folder inside an HDD, while the program sits in the OS disk (and SSD).

I have serious editing issues while I edit: after modifying anything at all the cpu ramps up at 98%/100%, making it impossible to edit further - when I try to edit something else while the cpu processes the first change, I have a lag between the action and the response form the program of 5-10 seconds circa (my last project was pretty heavy with color correction, titles, etc), all because the cpu is overloaded from the first modification.

I can't explain why there's this huge problem with the editing aspect and it has made that process the most tedious inside the program.

Can you please help me understand if it's something I can control or if I'm missing something? My pc is capable enough to do this and a lot more. Here are my specs

OS Name Microsoft Windows 10 Pro
Version 10.0.19042 Build 19042
System Type x64-based PC
Processor AMD Ryzen 7 3800X 8-Core Processor, 4200 Mhz, 8 Core(s), 16 Logical Processor(s)
GPU Nvidia Geforce GTX 970
BaseBoard Manufacturer ASUSTeK COMPUTER INC.
BaseBoard Product TUF B450-PLUS GAMING
Platform Role Desktop
Installed Physical Memory (RAM) 32.0 GB

I haven't done any proxies.

Note that the only overloaded thing is the CPU, while everything else seem to work just fine, with very low temperatures.
If it's of any use, I can post a video of this.

Get Studio and see your GPU doing the work. But then, yours might be stressed anyway with 4K, being 7 years old and having only 4 GB VRAM.
Or convert before editing to a format like Cineform or DNxHR.

The free version relies on your CPU much more. The simplest thing is the one thing you haven't done. Use proxies.

If you don't want to. Get the Studio version and yes likely upgrade your GPU.

I have a rule of thumb that applies here.

1. If you shoot H.264, edit with proxies.
2. If you don't want to use proxies, don't shoot H.264.

(I'm partial to using Cineform Optimized Media at 1/4 resolution for my H.264 clips.)