With HDT v1.5.0 MahApps.Metro was updated to 1.5.0, which sadly breaks the settings button in your case.
7:26:51 PM|Error|PluginWrapper.OnButtonPress >> Graveyard
System.MissingMethodException: Method not found: 'Void MahApps.Metro.Controls.Flyout.set_Header(System.String)'.
at HDT.Plugins.Graveyard.SettingsView.CreateSettingsFlyout()
at HDT.Plugins.Graveyard.SettingsView.get_Flyout()
at HDT.Plugins.Graveyard.GraveyardPlugin.OnButtonPress()
at Hearthstone_Deck_Tracker.Plugins.PluginWrapper.OnButtonPress() in D:\GitHub\Hearthstone-Deck-Tracker\Hearthstone Deck Tracker\Plugins\PluginWrapper.cs:line 144
With HDT v1.5.0 MahApps.Metro was updated to 1.5.0, which sadly breaks the settings button in your case.
Original issue on HDT: https://github.com/HearthSim/Hearthstone-Deck-Tracker/issues/3453