there are literally dozens and dozens of threads on this same question
1. don't ignore pinned post in this forum on posting OBS log
2. OBS Studio preview window and other sources all processing once OBS Studio is opened. Recording/Streaming is irrelevant. So if your OBS settings overwhelm your PC (either PC under-powered, settings, or driver update/change), then system slowness (due to some combination of RAM swapping, disk drive i/o queue backlog, CPU or GPU bottleneck, etc) is TO BE EXPECTED
a little hardware resource utilization monitoring goes a long way
