Upload Image/File Modal Empty, Potential JS Error in index.php?

Sorry for another potentially simple question. I’ve successfully managed to upgrade to EE 5.3.2, and everything seems to be working 99% correctly. Only two issues needed to be corrected. The first was that I needed to update the directory of emoticons/emojis in my settings. The second, however, seems to be that the image upload modal in my Create New Entry page will not work.

This is what I’m getting when I click on the icon to upload an image into any text field where images are permitted/intended.

There is a JavaScript error that I’m not sure is at fault or not. It occurs on index.php line 722 for me. The error is:

Unfortunately, it’s not the most clear error, which is one of the reasons I don’t know how to search for info on it. I have no clue if this is related to the empty modal or not, but it seems like something I should look into. The specific error in Chrome’s console is:
GET http://www.url.com/system/index.php?S=a4a3cfc8698b1994e6b6b14b73300c66&D=cp&C=javascript&M=combo_load&file=cp/global_end,cp/files/picker,fields/textarea/cp,cp/date_picker&v=1600791531 net::ERR_ABORTED 406 (Not Acceptable)

I wish I had a more clear question to ask. If anyone can help me out, please do. Thanks!