A better example of an upgrade file.

upgrade_example.php

<?php

/* Exit if accessed directly. */
defined( 'ABSPATH' ) || exit;

// Require WordPress Upgrade.
require_once ABSPATH . 'wp-admin/includes/upgrade.php';

function upgrade_v2() {

  global $wpdb;
  $current_version = get_option( 'my_plugin_version', '1.0' ) ?? '';

  if ( version_compare( $current_version, '2.0', '<' ) ) {

      // $charset_collate = $wpdb->get_charset_collate();

      // Example: Add Clean Index.
      // add_clean_index( $wpdb->posts, 'post_name' );
      // drop_index( $table, $index );

      // Maybe Add, Drop or Check Column.
      // maybe_add_column( $table_name, $column_name, $create_ddl );
      // maybe_drop_column( $table_name, $column_name, $drop_ddl );
      // check_column( $table_name, $col_name, $col_type, $is_null = null, $key = null, $default = null, $extra = null );

      // Maybe Create Table.
      // maybe_create_table( $table_name, $create_ddl );

      // Maybe Convert Table to UTF8MB4.
      // maybe_convert_table_to_utf8mb4( $table );

      // delete_option( string $option );
      // delete_transient( string $transient );

      // Flush Rewrites & Clear Cache.
      $flush_rules = flush_rewrite_rules() ?? '';
      $cache_flush = wp_cache_flush() ?? '';

      $updated_version = update_option( 'my_plugin_version', '2.0' ) ?? '';

      $results = array(
        'current_version'         = $current_version,
        'updated_version'         = $updated_version,
        'actions' => array(
          'flush_rewrite_rules'     = $flush_rules,
          'cache_flush'             = $cache_flush
        )
      );

      return $results;

  }
  
}