This add-on lets you easily toggle on WP_DEBUG and related constants. Once the add-on is enabled, it appears in the Tools tab in a sub-tab for each site.
WP Debug Toggler for Local by Flywheel
Tab view with nothing enabled
Enabling only WP Debug
Enabling WP_DEBUG and WP_DEBUG_DISPLAY
Enabling WP_DEBUG_LOG gives you a log viewer and a way to manage the log (clear, refresh and go to file)