Ensure some panels are "Always On".

wp-always-on-panels.js

// Subscribe to changes in the wp.data redux store.
wp.data.subscribe( () => {

	// An array of "Always On" panel (metabox) ids to disallow disabling.
	const alwaysOn = [];

	// Current panels preferences
	const panels = wp.data.select( 'core/edit-post' ).getPreference( 'panels' );

	// Loop over the panels object.
	for ( const id in panels ) {

		// Only target panels in the always alwaysOn array.
		if ( panels.hasOwnProperty( id ) && alwaysOn.includes( id ) ) {
			const panel = panels[ id ];

			// Only perform the actions with panels with enabled property.
			if ( panel.hasOwnProperty( 'enabled' ) ) {

				// If panel is disabled, enable it.
				if ( ! panel.enabled ) {
					wp.data.dispatch( 'core/edit-post' ).toggleEditorPanelEnabled( id )
				}
			}
		}
	}
} );