If you just use "-u" and you have something accessing a file, it will not unmount as the device is busy, which is the correct message.
'If you use -uz, it'll unmount and kill the process once the filesystem is not in use:
felix@gemini:~$ cd /Test
felix@gemini:/Test$ fusermount -u /Test
fusermount: failed to unmount /Test: Device or resource busy
felix@gemini:/Test$
felix@gemini:/Test$
felix@gemini:/Test$ fusermount -uz /Test
felix@gemini:/Test$ ps -ef | grep "Test"
felix 7256 7192 0 04:06 pts/0 00:00:00 rclone mount gcrypt: /Test
felix 7491 7361 0 04:07 pts/1 00:00:00 grep --color=auto Test
felix@gemini:/Test$ cd
felix@gemini:~$ ps -ef | grep Test
felix 7510 7361 0 04:07 pts/1 00:00:00 grep --color=auto Test
felix@gemini:~$
If you kill the process, you do have to clean it up:
felix@gemini:~$ cd /Test
-bash: cd: /Test: Transport endpoint is not connected
felix@gemini:~$ fusermount -uz /Test
felix@gemini:~$
felix@gemini:~$ cd /Test
felix@gemini:/Test$ ls
felix@gemini:/Test$ cd
felix@gemini:~$ cd /Test
felix@gemini:/Test$ ls