Critical Error-plugins are deactivated

I’m using WordPress for the first time. A few days ago I installed the latest version, picked a theme and started customizing it. I am using Projectfx and pagelayer.

All was going well until yesterday when I got the critical error message, no email. I cannot log into my dashboard–I get the same critical error. I checked the core integrity and then tried to reinstall–it didn’t work. I tried to follow the instructions on wpbeginner and did get to my plugins folder and renamed it plugins.deactivated as suggested. Still nothing.

I have screenshots of all of this, but don’t know how to link them. I did copy the written bit, which was:
Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/cassandr/public_html/wp-includes/wp-db.php:1788 Stack trace: #0 /home/cassandr/public_html/wp-includes/wp-db.php(724): wpdb->db_connect() #1 /home/cassandr/public_html/wp-includes/load.php(561): wpdb->__construct() #2 /home/cassandr/public_html/wp-settings.php(124): require_wp_db() #3 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/wp-cli/php/WP_CLI/Runner.php(1291): require('/home/cassandr/...') #4 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/wp-cli/php/WP_CLI/Runner.php(1212): WP_CLI\Runner->load_wordpress() #5 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/wp-cli/php/WP_CLI/Bootstrap/LaunchRunner.php(23): WP_CLI\Runner->start() #6 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/wp-cli/php/bootstrap.php(77): WP_CLI\Bootstrap\LaunchRunner->process() #7 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/wp-cli/php/wp-cli.php(27): WP_CLI\bootstrap() #8 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/wp-cli/php/boot-fs.php(17): require_once('/usr/local/cpan...') #9 /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/wpt-wp-cli.php(31): require_once('/usr/local/cpan...') #10 Command line code(1): require('/usr/local/cpan...') #11 {main} thrown in /home/cassandr/public_html/wp-includes/wp-db.php on line 1788 Error: There has been a critical error on this website.Learn more about troubleshooting WordPress. There has been a critical error on this website.

Thanks for any help.

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