The following diagram, from About ELevate project | AlmaLinux Wiki, suggests that if you’re planning to use ELevate, you must first go from Cent 7 to Rocky 8, and then from Rocky 8 to Rocky 9.
I personally have only ever used Leapp (ELevate’s upstream) to go from RHEL7 to RHEL8, for the specific case of updating Katello when the project stopped supporting EL7, and it took a fair bit of manually removing unsupported stuff and adding back what we wanted to keep afterwards. I’m not sure how well upgrading major EL versions works in the general case. You may find that enough has changed between EL7 and 9 that you end up having to do just as much work to make your application go as you would have setting up a new EL9 installation and migrating to it.
Absolutely make sure you have bare-metal backups or VM snapshots if you decide to attempt this.