In QGIS 3 I couldn't find any suitable answer for my struggle. I have two layers with different objects (buildings from different areas). I want them to have same columns, but creating one by one is very time consuming, so I was wondering if there's easier solution to copy empty columns from one layer to another?
In the processing toolbox, search for Refactor fields.
Here the documentation (3.22).
You can select your layer to modify as
Input layer and load field from another layer (see the combo below under the Fields mapping list)