I have used Shotcut since 2018 and there are always issues with complicated effects on videos (only 1080p) making my program lag a lot, to the point where tasks like alinging video with music is an absolute chore to do. Bear in mind I do not edit 4k video, just 1080p 30fps and 60fps for YouTube.
Sometimes it is impossible to use, and today its ok (see video) compared to how it was sometimes.
The project shown in the recording only has effects such as colour grading, mask (from file) and size and position across 3 or 4 tracks.
Ryzen 5 1600 @ 3.6Ghz
GTX 1060 6GB
16GB DDR4 2133mhz RAM (yes I know this is slow but its all I had the money for at the time)
7200RPM 1TB HDD (where the video is pulled from) Seagate ST1000DM003-1ER162 (SATA)
128GB M.2 SATA SSD (boot drive) ADATA SU800NS38 (SATA (SSD))
I have tried to turn off multiple settings such as Real Time and Scrub Audio and used preview scaling at 360p, both with minimal increaes in performance. The OBS footage I input into Shotcut is just an MP4