Lagging preview

I have a problem with the preview in shotcut. he is laggin while i add clip which have above 30 sec. i tried to turn on 360 p scaling but it didnt work

computer specifiaction:
intel i3-10100f
8gb ram

If you do not also use proxies that is probably going to make things worse. Read the FAQ and Documentation - English

Also, what are the type and resolution of your video files?
Your computer (4 cores CPU, 8 gigs of RAM) is at the minimum end of the requirements for HD, and below the minimum requirements for 4K videos.