How do I disconnect all other users in tmux?

tmux a -dt <session-name>

a=attach
d=detach other clients (so only you can attach to this session)
t=target

You can use <prefix> D ^{(where prefix is C-b by default)}, to chose which clients to detach; it will also list they col/lines as well as the last used time. Note the uppercase D, i.e. Shift+d.

You could also use tmux's detach-client option

 detach-client [-P] [-a] [-s target-session] [-t target-client]
               (alias: detach)
         Detach the current client if bound to a key, the client specified
         with -t, or all clients currently attached to the session speci-
         fied by -s.  The -a option kills all but the client given with
         -t.  If -P is given, send SIGHUP to the parent process of the
         client, typically causing it to exit.

either from <prefix>:followed by detach [options] or on the command line inside tmux with tmux detach [options]