Hi, I keep receiving these errors too.
PHP 7.2; OJS 3.2.1-4
[13-Mar-2021 19:56:37 UTC] PHP Fatal error: Uncaught PDOException: could not find driver in /home/denqgtqu/public_html/ojs/lib/pkp/lib/vendor/illuminate/database/Connectors/Connector.php:70
Stack trace:
#0 /home/denqgtqu/public_html/ojs/lib/pkp/lib/vendor/illuminate/database/Connectors/Connector.php(70): PDO->__construct(‘mysql:host=loca…’, ‘denqgtqu_ojs’, ‘ut^6Y0,4.g}U’, Array)
#1 /home/denqgtqu/public_html/ojs/lib/pkp/lib/vendor/illuminate/database/Connectors/Connector.php(46): Illuminate\Database\Connectors\Connector->createPdoConnection(‘mysql:host=loca…’, ‘denqgtqu_ojs’, ‘ut^6Y0,4.g}U’, Array)
#2 /home/denqgtqu/public_html/ojs/lib/pkp/lib/vendor/illuminate/database/Connectors/MySqlConnector.php(24): Illuminate\Database\Connectors\Connector->createConnection(‘mysql:host=loca…’, Array, Array)
#3 /home/denqgtqu/public_html/ojs/lib/pkp/lib/vendor/illuminate/database/Connectors/ConnectionFactory.php(182): Illuminate\Database\Connectors\MySqlConnector->connect(Array)
#4 [internal function]: Illuminate\Database\Connectors\ConnectionFactory->Illumin in /home/denqgtqu/public_html/ojs/lib/pkp/lib/vendor/illuminate/database/Connection.php on line 664
I tried using PHP 7.3 ( as mentioned here) but raised another error 
[13-Mar-2021 20:02:26 UTC] PHP Fatal error: Uncaught Error: Call to undefined function PKP\Services\json_decode() in /home/denqgtqu/public_html/ojs/lib/pkp/classes/services/PKPSchemaService.inc.php:56
Stack trace:
#0 /home/denqgtqu/public_html/ojs/lib/pkp/classes/site/SiteDAO.inc.php(62): PKP\Services\PKPSchemaService->get(‘site’)
#1 /home/denqgtqu/public_html/ojs/lib/pkp/classes/site/SiteDAO.inc.php(42): SiteDAO->_fromRow(Array)
#2 /home/denqgtqu/public_html/ojs/lib/pkp/classes/core/PKPRequest.inc.php(490): SiteDAO->getSite()
#3 /home/denqgtqu/public_html/ojs/classes/i18n/AppLocale.inc.php(78): PKPRequest->getSite()
#4 /home/denqgtqu/public_html/ojs/lib/pkp/classes/i18n/PKPLocale.inc.php(140): AppLocale::getLocale()
#5 /home/denqgtqu/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php(131): PKPLocale::initialize(Object(Request))
#6 /home/denqgtqu/public_html/ojs/lib/pkp/classes/core/PKPApplication.inc.php(281): Dispatcher->dispatch(Object(Request))
#7 /home/denqgtqu/public_html/ojs/index.php(68): PKPApplication->execute()
#8 {main}
thrown in /home/denqgtqu/public_html/ojs/lib/pkp/classes/services/PKPSchemaService.inc.php on line 56