Changing renderer options don't apply automatically when using the Styling panel

[SrNetoChan]

One of the advantages of the Styling Panel is the fact that any changes are applied automatically and rendered on the map. When changing the settings on the Styling Panel, the user needs to click apply, even when the automatically apply option is selected.

[volaya]

looks like this was already an issue before porting to qgis3

Not sure how to fix it, but i would mark as no-fix and investigate the solution if we have time later