There is no rightclick.js file in Glitch’s sources, neither the adblocker’s.
Are you using any other extensions ?
If you don’t know about the rightclick.js, just hover on its name in the left of console until the URL appears under it then take a screenshot again, might be helpful to know the source of that file.
It’s the ‘Allow Right-Click’ extension that’s producing that error in the console, but the sidebar still shows for me with it enabled so it doesn’t seem to be the cause either.