The manual option requires fiddling with some permissions on a normal OpenSSH system. Here're the relevant bits for the servers I manage:

/etc/ssh/sshd_config

AllowGroups ... ssh-ftp-only ...

...

Match Group ssh-ftp-only
        ChrootDirectory %h
        ForceCommand internal-sftp -d upload
        PermitTTY no
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Then add your user to that group, and set their shell to /usr/local/sbin/scponlyc if available.

Then you need these permissions on their home directory:

drwxr-x--- 5 root   user     4096 Jun 12  2017 /home/user/
drwx------ 2 root   root     4096 Nov  7  2016 /home/user/.ssh
drwxr-xr-x 2 user   user     4096 Feb 27  2020 /home/user/upload
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This is because letting them modify their own .ssh directory or create a /lib directory within their chrooted home would also let them escape the chroot, so ssh checks for those cases before letting them write anything.

When they connect, the current directory will be the chroot's /upload directory, and that will be the only directory they can write.