The program highlights the page style (or paragraph style) selected, but it is so dark grey it practically blocks out the name of the style selected. There must be a way to lighten that highlight, but I can’t find it.
This is a matter of “theme”. You probably selected a dark one in Finder. Try another one to see if there is a difference. If so, you can afterwards tailor LO applications colors in Preferences, LibreOffice>Personalization (LO theme) or LibreOffice>Appearance to override the offending ones.