Fresh Installation Fatal Error

Hello, I am trying to install PressBooks to a freshly created wordpress site. I encountered a fatal error when I tried to activate the plugin. It saids,

Parse error : syntax error, unexpected ‘?’, expecting variable (T_VARIABLE) in /home3/gogoyued/public_html/pressbooks/wp-content/plugins/pressbooks/vendor/sentry/sentry/src/functions.php on line 25

FYI, I am using Bluehost and PHP version is 7.3.6.

Any thoughts?