Prevent updating for specific WordPress plugins.

prevent-plugin-update-dot-org.php

<?php
// Prevent updating of specific dot org plugins.
add_filter(
	'site_transient_update_plugins',
	function( $transient ) {
		$plugin_arr = [ 'test-plugin2/test-plugin2.php', 'akismet/akismet.php' ];
		foreach ( $plugin_arr as $plugin_file ) {
			if ( isset( $transient->response[ $plugin_file ]->id )
				&& false !== strpos( $transient->response[ $plugin_file ]->id, 'w.org/plugins' )
			) {
				unset( $transient->response[ $plugin_file ] );
			}
		}

		return $transient;
	},
	99,
	1
);

prevent-plugin-update.php

<?php
// Prevent updating of specific plugins.
add_filter(
	'site_transient_update_plugins',
	function( $transient ) {
		$plugin_arr = [ 'test-plugin2/test-plugin2.php', 'akismet/akismet.php' ];
		foreach ( $plugin_arr as $plugin_file ) {
			if ( isset( $transient->response[ $plugin_file ] ) ) {
				unset( $transient->response[ $plugin_file ] );
			}
		}

		return $transient;
	},
	99,
	1
);