Instead of Afterburner.
Ciould you have a look into Taskmanager’s CPU load?
Test on my side
6th gen intel notebook, windows 10, dedicated GPU disabled, Krita 5.3.
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A4, 300 ppi canvas in Krita
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Basic-1 brush in Krita @ 40 px
Making a single stroke for about 20 seconds
CPU load:
Around 8% (with short spikes up to 15%) (OpenGL acceleration active).
CPU temps 35 to 40 degree celsius. (measured with free HWINFO - https://www.hwinfo.com/)
Fans do not even spin up.
Your system should not have an issue like overheating in this test case.
I tested with a fresh clean install of Krita 5.3 (but i guess Krita 5.2.x would be similar). No custom settings except from setting to OpenGL acceleration. No plugins, no extra brush packs etc. I used the notebook’s touchpad, pen tablet was not attached.
EDIT: Same test but with 600px air brush:
CPU load around 20%
CPU temps around 45 degree celsius.