Apply anti-aliasing settings on the fly.
I use current development version of Xfce (4.13),which is default in Fedora 30. I noticed that when changing anti-aliasing options for fonts in Xfce Appearance Settings, these settings are not applied on-the-fly. In that application a workaround is to check or uncheck the 'Force DPI' option and this applies the chosen anti-aliasing settings.
I opened a bug report in https://bugzilla.xfce.org/show_bug.cgi?id=15643 and it was said that this behaviour is for GTK3 only (GTK2 used to work) and is common also to MATE and GNOME DE's. So it was suggested that I opened this bug report for GTK.