We’ve used Katalon to test Mendix apps. It’s also based on Selenium.
There are many tools that allow you to automate tests in browsers. In the past, I've been involved in projects where this was done using Selenium, but that was pretty hard. I know customers that use Ranorex, and some who use LoadRunner. I have a number of colleagues who really like LoadRunner, since it works pretty well for recording scenario's in Mendix apps.