Q1: when accessing RIMS, the page gives this message “The requested URL /alpha was not found on this server”

Fatal error: Uncaught Error: Call to undefined function twenty_twenty_one_post_thumbnail() in /usr/local/www/RIMS21/wp-content/themes/drc/template-parts/content/content.php:22 Stack trace: #0 /usr/local/www/RIMS21/wp-includes/template.php(732): require() #1 /usr/local/www/RIMS21/wp-includes/template.php(676): load_template('/usr/local/www/...', false, Array) #2 /usr/local/www/RIMS21/wp-includes/general-template.php(204): locate_template(Array, true, false, Array) #3 /usr/local/www/RIMS21/wp-content/themes/drc/archive.php(55): get_template_part('template-parts/...', 'excerpt') #4 /usr/local/www/RIMS21/wp-includes/template-loader.php(106): include('/usr/local/www/...') #5 /usr/local/www/RIMS21/wp-blog-header.php(19): require_once('/usr/local/www/...') #6 /usr/local/www/RIMS21/index.php(19): require('/usr/local/www/...') #7 {main} thrown in /usr/local/www/RIMS21/wp-content/themes/drc/template-parts/content/content.php on line 22