You’re just going to be doing, manually, what the CPU scheduler is doing automatically.

What the other guy said, the task scheduler already assigns processes to cores depending on what is suitable.

What you might look into, if you want to reduce thermal throttling, is undervolting. By reducing the voltage being used by your CPU, it'll run cooler.

I almost always give undervolting a go on laptops. Saves battery, reduces temps, potentially even improves performance.

On a modern laptop undervolting probably isn’t an option, but you can try to reduce your CPUs clock speeds.

My old thinkpad has a PL1 of like 100 watts normally, 50 watts in game, but it drops all the way down to just 25 watts after a while. If I can reduce my CPUs clock speeds so it rarely exceeds 35 watts in game then I can maintain that higher power level almost indefinitely. Maybe try seeing if your laptop is doing something similar?