Clip/grdclip arbitrary polygon

I have irregular data points (long, lat, values). The values are irregular that obviously produced “bad” interpolated values far from the points. How can I mask those “bad” interpolated areas? Any pointer, please?

Yes, but sorry not the one you may be expecting.
https://flint.soest.hawaii.edu/t/forum-tips-tricks-create-a-good-post/2585/4