Display all form errors in the popup.

um_display_all_form_errors.php

<?php

/**
 * Display all form errors in the popup.
 */
add_action( 'um_after_form', function () {
	if ( ! empty( UM()->form()->errors ) ) {
		$error_text = implode( '<br>', UM()->form()->errors );
		?>
		<div id="um_form_errors" style="display:none;">
			<a href="javascript:void(0);" data-action="um_remove_modal" class="um-modal-close" aria-label="Close"><i class="um-faicon-times"></i></a>
			<div class="um-modal-header">Form errors</div>
			<div class="um-modal-body"><?php echo $error_text; ?></div>
		</div>
		<script type="text/javascript">
			jQuery( window ).load( function() {
				um_new_modal( 'um_form_errors', 'normal', false, '' );
			} );
	  	</script>
		<?php
	}
} );

This works on the profile edit.

Expected result

See an alternative solution in the article Display all form errors below the form.