Unable to drag files from desktop across desktops now that an external screen has been added

This was a question asked previously, but I'm having the same issue - the answer given was not a solution for me, any help?

I have an M1 Studio, I have chosen to "extend displays" and the displays have their own spaces.

I frequently will drag files saved on my desktop across desktops to a full-screen window (i.e. to attach images to email). This has always worked beautifully. Now that I've added an additional screen, I can no longer use this function in the same way. I can drag items to the external screen, but I cannot drag them between desktops on the MacBook. As soon as the external screen is disconnected, the functionality returns.