The clues are there for you. Bonus points if you can find the full original publication citation.
Fatal error: Uncaught TypeError: count(): Argument #1 ($value) must be of type Countable|array, bool given in /home/jmcclurken/subdomains/courses/adh20/wp-content/plugins/custom-twitter-feeds/inc/CtfFeed.php:1856 Stack trace: #0 /home/jmcclurken/subdomains/courses/adh20/wp-content/plugins/custom-twitter-feeds/inc/CtfFeed.php(1856): count(false) #1 /home/jmcclurken/subdomains/courses/adh20/wp-content/plugins/custom-twitter-feeds/custom-twitter-feed.php(414): TwitterFeed\CtfFeed->getTweetSetHtml() #2 /home/jmcclurken/subdomains/courses/adh20/wp-includes/shortcodes.php(434): ctf_init(Array, '', 'custom-twitter-...') #3 [internal function]: do_shortcode_tag(Array) #4 /home/jmcclurken/subdomains/courses/adh20/wp-includes/shortcodes.php(273): preg_replace_callback('/\\[(\\[?)(custom...', 'do_shortcode_ta...', '[custom-twitter...') #5 /home/jmcclurken/subdomains/courses/adh20/wp-includes/class-wp-hook.php(326): do_shortcode('[custom-twitter...') #6 /home/jmcclurken/subdomains/courses/adh20/wp-includes/plugin.php(205): WP_Hook->apply_filters('[custom-twitter...', Array) #7 /home/jmcclurken/subdomains/courses/adh20/wp-includes/widgets/class-wp-widget-custom-html.php(150): apply_filters('widget_text', '[custom-twitter...', Array, Object(WP_Widget_Custom_HTML)) #8 /home/jmcclurken/subdomains/courses/adh20/wp-includes/class-wp-widget.php(394): WP_Widget_Custom_HTML->widget(Array, Array) #9 /home/jmcclurken/subdomains/courses/adh20/wp-includes/widgets.php(845): WP_Widget->display_callback(Array, Array) #10 /home/jmcclurken/subdomains/courses/adh20/wp-content/themes/activello/sidebar.php(23): dynamic_sidebar('sidebar-1') #11 /home/jmcclurken/subdomains/courses/adh20/wp-includes/template.php(810): require_once('/home/jmcclurke...') #12 /home/jmcclurken/subdomains/courses/adh20/wp-includes/template.php(745): load_template('/home/jmcclurke...', true, Array) #13 /home/jmcclurken/subdomains/courses/adh20/wp-includes/general-template.php(136): locate_template(Array, true, true, Array) #14 /home/jmcclurken/subdomains/courses/adh20/wp-content/themes/activello/archive.php(108): get_sidebar() #15 /home/jmcclurken/subdomains/courses/adh20/wp-includes/template-loader.php(106): include('/home/jmcclurke...') #16 /home/jmcclurken/subdomains/courses/adh20/wp-blog-header.php(19): require_once('/home/jmcclurke...') #17 /home/jmcclurken/subdomains/courses/adh20/index.php(17): require('/home/jmcclurke...') #18 {main} thrown in /home/jmcclurken/subdomains/courses/adh20/wp-content/plugins/custom-twitter-feeds/inc/CtfFeed.php on line 1856