How to disable service workers in Safari? Is there a way to disable Service Workers completely in Safari (as a user)?
This is for Safari 12.0.3, the experimental feature set is different in different Safari versions.

Enable the Safari developer menu. Safari Preferences > "Advanced" pref pane > "Show Develop menu in menu bar" checkbox at the bottom.

Then, in Develop menu, go to "Experimental Features" menu item and disable "Service Workers" in the sub menu.