WordPress Widget dropdown arrows are not working
Here is a curious thing.
I have WordPress in a few subdomains. And all but one worked fine.
I went to edit a sidebar widget (as you do) and the drop down arrows were not working… This is quite serious as how on earth do you get to the content? For many manually editing the Database is not for the fainthearted! Well in actual fact for the VAST majority of people there is a simple solution before you begin to start disabling plugins and switching your theme/s.
Try a different browser. For me it was Google Chrome that was bugged (maybe its an update issue?). So I switched Microsoft Edge and worked perfectly. This demonstrates one thing that it is NOT WP that is always at fault, so butchering WordPress is a hole you do not wont or need to go down when it maybe unnecessary. Remember there are plenty of free browsers out there from Firefox to Opera. So before you do ANYTHING recommended by WP requiring you to make changes to your install such as disabling plugins (sheesh! :/) try a different browser and be aware that Vanilla Browsers (with NO ADDONS or EXTENSIONS or temporarily disable the ones you have got) are a better bet to check this.
If this fails then go to Worpress.org and report it.