According to the changelog, this should be included in the dnf-plugins-core: "new plugin post-transaction-actions (RhBug:967264)" That does not appear to the case. Since nothing is really broken I will not provide negative karma.
No login screen appears after the update. Tried on bare-metal and a VM. Downgrading mutter solves it. I see a lot of "Fatal IO error 11 (Resource temporarily unavailable) on X server :0." messages. I'll see if I can figure out what is wrong and log a bug in bugzilla later today.
When using xorg-x11-server-1.20.5 my external monitor (Dell U2515H) stays blank. xrandr/settings does see the monitor correctly but you can not show any content on it. I usually have the external monitor set to being the primary and the internal laptop (Dell Latitude E5570) display to secondary, below the primary. Tried removing monitors.xml and the external display shortly fires up but then goes blank again. Filed a bug already: https://bugzilla.redhat.com/show_bug.cgi?id=1723715