A custom theme could be interfering with this. I would first suggest checking if it works when you have the default theme selected and custom snippets disabled.
The other option you can try is setting a different Window frame style:
I had the same issue on Linux. My solution was to change to the native frame option so my window manager works.
Thank you! The problem solved if I switch to native frame.
I had the same issue on mac and then noticed that it was only happened on one of my two vaults. The one that I could not drag was running obsidian nord and the other was default, issue went away after changing back to default.