Rainbow cursor every time on safari
The rainbow cursor indicates that the application in question is blocked because the system watches for it saying it’s ready for things like keyboard input.
The page you are visiting is causing an entire app to block so that’s a problem for sure if you need that page to work before it gets fixed. It’s normal and expected the system lets you know one app is blocked, so you can go do other tasks in other apps and eventually force Safari to quit when you tire of waiting for it.