Sharpen won't work anymore?

[rich2005]

That menu entry, Select -> Sharpen is only active when there is an active selection. Do you have an active selection ?

See the Gimp Docs https://docs.gimp.org/2.10/en/gimp-selec...arpen.html

Maybe you want one of the filters from Filters -> Enhance such as Unsharp mask or a wavelet decompose.