I purchased this software to do one simple thing: edit screen recordings of my laptop (me doing a lecture through a PowerPoint) to post it online.

problem is, every time I export the 20 minute recording (200mb - a 1080p, 30 FPS clip) - the video preview is very bad, it often goes completely black, and if I ever dare to cut/clip a portion of the video on the timeline - the entire video preview goes pixelated and I can’t see a thing I’m doing.

I have a new 2020 gaming laptop, Ryzen 7 4000 series processor, 8 core, 16 GB of RAM, 2060 graphics and so on. So it should be capable of editing a fairly short screen recording.
 

Any tips? I feel seriously disappointed with my purchase.