How to enable swatches globally to all variable products?

Yes, It can be done by using a global attribute.

Just follow these simple steps.

1: WooCommerce-> product->attribute.

2: Click on attribute(color)-> then all variations are listed (black, blue, black-silver, black-green etc).

3: Click on configure terms-> as you click on that all variation will list.

4: Select any WooCommerce variation -> click on edit(button)-> there is an option “Display Type” from there you can select thumbnail-image/color/text which you want to display on the front end.

5: Now this setting work globally for all global attributes and swatches will show on all products.