What is the proper compression for a single channel grayscale texture?

Been trying to get a proper single channel grayscale texture for a while but haven’t quite pinpointed the right way. Anyone clue me in? Thanks much.

Not sure what was causing you confusion here.

Perhaps this?


But “Grayscale” seems to be uncompressed. “Alpha” indeed seems to be the right one to use, but then the name “Alpha” is confusing if someone wonders which method to use for a roughness texture, for example.