Shotcut running like butt even with a great PC

What are the project Video Mode properties set to? You can find out by clicking on Output, then Properties.
2023-05-03_12-05-42

Click on the clip in the timeline, then Properties. What are the clip properties?

Having a mismatch of FPS (Frames per second) can cause major issues.

Is your media on the Samsung Evo 970 NVME drive or the HDD?

  • Samsung NVME read/write speeds: Sequential read and write performance levels of up to 3,500MB s and 3,300MB s
  • 4tb Firecuda HDD: Obtain maximum sustained transfers at 255MB/s