When I said I deleted a file, it means I right-click the file in Windows File Explorer, then 'Delete'.
If I start PC with external drive already plugged in, a file I delete goes into Recycle Bin. If I then unplugged the external drive and then plug in again, Avast makes it a flash drive without Recycle Bin. When I delete a file, Windows asked whether I want to delete it permanently meaning there is no Recycle Bin which is behaviour of a flash drive.
With Avast 22.6 Beta earlier, even if unplug and plug in again the drive, there was a Recycle Bin. Too bad there is no offline installer for beta versions so that I can go back to 22.6 Beta. The stable version 22.6 also got this problem but not 22.6 Beta.