Instead of styling every shape individually, you can style one, then apply that style to multiple selected shapes via the format panel.
- Update the style of one of the shapes or connectors in your diagram. Note that shape and connector styles must be copied and pasted separately.
- Select that shape or connector, then in the Style tab of the format panel, click on Copy Style.
- Select the other shapes or connectors that you want to apply this style to. In the Style tab, click on Paste Style.
Tip: There are many shortcuts for working with styles in diagrams.net.