Do you get the same performance if files are on your C drive?
I know you posted extensively on the other thread. Have you ever tried testing Shotcut without any Anti-Virus programs running?
I’m willing to test a clip and follow your same filter and export settings, but in my opinion, we would have a world of difference because I am not running any anti-virus programs. Nor am I running One-Drive.
But for the sake of science, pick a clip from here: https://pixabay.com/ Create a project file from that 1 clip and upload your MLT file here, so I and possibly others will test the same exact settings. You will need to share your export settings in text.