Darktable 5.0: Blur using JPG source files still locks CPU + LightTable file view issues

That has nothing to do with the blurs module.
As Mica mentioned, apply mask refinement.
See examples in recent threads, e.g.

Forget the brush (I mean, don’t rely on it as your only masking tool). I know you are familiar with it, but darktable can do so much more.

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