High load with low cpu performance and premiere pro lagging

I’m using a MacBook Pro with the M3 Pro chip. When I started editing my first video in Premiere Pro — a simple 4K 10-bit S-Log video — I noticed that the performance was lagging, even though I only added four text layers.

I checked the CPU usage and found it to be low, doesn't go above 20% but the video is so lagging specail after using replace with after effect option to make and effect for part of the video

so I’m not sure why Premiere Pro is struggling with such a basic project or my new mac have problem??