I’ve had good results by using Auto-mask over the key subject, then inverting the mask (so that it now applies to everything except the key subject) and then applying a small amount of blur to the (inverted) mask … so that the background appears slightly out-of-focus.
I agree, tho, that it can be tricky to get the right amount of blur when the slider effect is so strong … this difficulty could be alleviated if adjustment of Local Adjustment sliders was consistent with ability to adjust Global sliders - as requested/proposed here.
Regards, John M