Auto-Styling QGIS vector layers symbology
Multi-layer style copying/pasting
If all or most of the layers you want to style share the same symbology, you can:
- Apply a pre-saved style to one layer by loading a style from file
- Right-click on the layer in the layer list, select
Styles->Copy style->All style categories - Always in the layer list select all the layers you want to apply the same style to, then
Styles->Paste style->All style categories
You can try use Set style for vector layer algorythm.
Adventage of that solution is that you can make it batch processing/save that to for later reuse.
I think what you are looking for are Map themes. You can access map theme manager by clicking an eye symbol, in the upper icons row, in layers panel. Then simply choose 'add theme'. All the styling and visibility settings for layers, in the layer panel list, will be saved, a new entry will appear in the theme list. You can also use named Map themes to style Maps in layouts by one click. Here is the link to documentation section: https://docs.qgis.org/3.4/en/docs/user_manual/introduction/general_tools.html#configuring-map-themes
Besides visibility, map theme will also store layer's symbology, but you have to save it as named style first.
To do so, right-click on the layer's row in legend panel, than choose styles>Add, you have to name the current style. Confirm and you will see it on the list above color picking wheel. Afterwards you can change the layer's symbology and save the new configuration in the same way. When there is more than one style on the list, you can switch symbology by picking the right entry by name.
When you will define a new map theme it will store current visibility settings as well as currently active named style.