pmpro-read-only-profile-edit-fields.php

<?php
/**
 * This recipe assigns the readonly attribute to specific fields on the profile edit page.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

 function read_only_profile_edit_fields_javascript() {
	global $current_user;

	// Add field names to be set as readonly to this array.
	$read_only_field_names = array( 'first_name', 'last_name', 'display_name', 'user_email' );

	// Bail if administrator or not logged in user.
	if ( ! is_user_logged_in() || current_user_can( 'manage_options' ) ) {
		return;
	}

	$reserved_field_names = array( 'user_email', 'display_name' );

	// If read only field values that are not reserved field names are empty for user meta, drop the name from the array.
	foreach ( $read_only_field_names as $key => $field_name ) {
		if ( ! in_array( $field_name, $reserved_field_names ) && empty( get_user_meta( $current_user->ID, $field_name, true ) ) ) {
			unset( $read_only_field_names[ $key ] );
		}
	}

	// Bail if no read only fields.
	if ( empty( $read_only_field_names ) ) {
		return;
	}

	?>
	<script>jQuery(document).ready(function ($) {
		<?php
		foreach ( $read_only_field_names as $field_name ) {
			?>
			$('#<?php echo esc_js( $field_name ); ?>').attr('readonly', true);
			<?php
		}
		?>
		});
	</script>
	<?php
}

function read_only_profile_edit_fields_init() {
	// We're on the WP Dashboard but not an admin.
	global $pagenow;
	if ( is_admin() && 'profile.php' === $pagenow ) {
		add_action( 'admin_footer', 'read_only_profile_edit_fields_javascript' );
	}
}
add_action( 'init', 'read_only_profile_edit_fields_init' );

function read_only_profile_edit_fields_wp() {
	// Bail if PMPro Core not active
	if ( ! defined( 'PMPRO_VERSION' ) ) {
		return false;
	}
	// We're on the front end profile edit page.
	global $pmpro_pages;
	if ( is_page( $pmpro_pages['member_profile_edit'] ) ) {
		add_action( 'wp_footer', 'read_only_profile_edit_fields_javascript' );
	}
}
add_action( 'wp', 'read_only_profile_edit_fields_wp' );

For toggling the readonly status for custom user fields only see https://gist.github.com/ipokkel/867fb8103f7e789ae089e55cbc93a9dc