HOW CAN I RESTORE A FILE IN IMAC IN TRASH WITH NO ACCESS TO IT?

Boot into Safe Mode by booting with the Shift key held down and try to delete the folder from there.  Reboot normally.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Restore it from your Time Machine backup!

Where did the file come from? Also check your shift key as it appears stuck.

Try a cmd-drag.

You do not want to try to delete a file from the Time Machine drive via the Finder. If you get it to the Trash bin it will be stuck there until you erase the TM drive and start over afresh.

Hold down the command key while you drag the item out of the trash.

But where did the folder come from?

What's the name of the folder and did you install a system update just prior to it appearing?