...when using the Google Chrome browser (on both Mac and Windows), if I go to
https://teslamotorsclub.com/tmc/forums/model-x.84/create-thread and try to create a new post, hovering my cursor over the "Create Thread" button hi-lights the "Upload a File" button instead. So I can't create a new thread using Chrome.
If I'm posting a reply to a thread instead of creating a new thread, clicking on "Post Reply" and "More Options" work fine, but once on the "More Options" screen, hovering my cursor over "Reply to Thread" instead hi-lights the "Upload a File" button again. "Preview..." works on that screen, but once on the "Preview" screen, "Reply to Thread" still hi-lights "Upload a File" (and "Preview..." still works).
I don't have any unusual extensions, and there's no ad blocking in effect, so I don't know why you can't reproduce this behavior on your end. (I don't have this problem on Safari, Firefox, Internet Explorer, or MS Edge.)