PD will typically use all available cores, but there are many edits that simply cannot be processed and previewed in real time by even the most powerful CPU or system.
Lowering the preview resolution will help for some of those situations and using shadow files can also help, but for the most compute-intensive edits you'll need to pre-produce the affected sections first then import the produced clips and place them in your main project.
Even thought it might seem like that will add a lot of time upfront, it will save you a lot of frustration and likely will actually save you time overall.
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