USB flash drives cannot be ejected
Some flash drives allow themselves to be ejected in any of the ordinary ways; with others, particularly large-capacity ones, if I either drag them to the trash or right-click them and select 'Eject', a message appears after a while, saying that the drive cannot be ejected because the Finder is using it, even though the Finder is not using it in any obvious way. I then have to 'Force Eject'.
I know there has been correspondence about similar problems, but the details of mine are a little different and I thought it was worth posting this question.
My device is a Mac Mini (late 2012) with MacOS 10.16.6 (Mojave).