Up until and including 20.12.3, selecting text in Konsole was very apparent (IIRC, the foreground and background colours were switched). With 21.04.0, it's very difficult to even see that text is selected at all: it seems the only visual change is a slightly less dark background colour. I don't see any way to get the original behaviour in settings/profile.
*** This bug has been marked as a duplicate of bug 435309 ***