P: Artifacts on grouped layers (Win10)

I wouldn't say so. Don't you see it in the PSD I posted? Try to clip/unclip the top adjustment layer.
Here are 2 images for comparison. https://www.dropbox.com/sh/hib3pcrh0o38ly8/AAAL2jfB5mh9WZkRu1revaHIa?dl=0

Sorry, I had too many issues with 21.1.x therefore I returned to 21.0.3.
Actually, I found out to put the layer effects to the groups folder. With that, the shadows are good.

If 21.1.1 doesn't fix your issue, please post your PSD for us to troubleshoot. Thx.

Roman, is this what you're seeing with your issue? https://feedback.photoshop.com/photoshop_family/topics/disrupt-edges-when-painting-masks-under-adjus...

Your issue should be remedied in 21.1.1 update.

Same here (Mac OS, problem first recognized with PS 21.0.3.) with layer groups containing layers with layer effects like drop shadow. Creating an adjustment layer over the group and clipping it with the group, cutting edges appear on the drop shadow.