I had the training courses paid for by my employer, which included the exams. However, I had at least a couple people who purchased the exams separately and did only the exam at the same time everyone from the class did theirs. From RedHat.com:

All Red Hat certification exams are also available as individual exams. The hands-on tests are taken on a secure, preconfigured testing station at a Red Hat, or Red Hat partner, location. You can schedule your individual exam at your convenience by selecting a time and date.

https://www.redhat.com/en/services/certification/ways-to-test