Problems/Questions with UR24C

I’m fairly new to sound engineering. I have only a very basic understanding. I record podcasts and music from time to time. Just upgraded my home studio to include a RODE Procaster into a CL1 into the UR24C.

I am having trouble outputting sound from my iMac desktop to the UR24C. After recording into QuickTime (not my typical practice, but just recording some quick tests) with the UR24C input, for some reason that I cannot understand, there is NO AUDIO when I play it back.

If I switch my computer audio output to the internal speakers, or my AirPods, or any other audio output, it plays the sound perfectly normal. However, when I switch the output back to the UR24C, I hear nothing. If I play something from another application, like Spotify or anything in a web browser, or on Zoom, pretty much any other audio output, it comes through the UR24C. It only happens in QuickTime, when I’m trying to play back what I just recorded.

HOWEVER, when I switch the UR24C output from Output 1- Switch to Output 2 - Stereo, the QuickTime audio comes through! BUT only in the left ear!!! What?!?! Why?!

I really don’t understand the split output at all. I don’t see any point in ever using the “Stereo” output where it puts my computer audio out one ear and I can’t even monitor the mic audio anymore. I don’t have any understanding of the difference between these and would love any kind of explanation.

Anyway, if anyone can help me figure out how to fix the output from my computer so that it plays correctly out of my UR24C while I can monitor the mic also and not have it come out of the left speaker only, it would be much appreciated!!!