i have exactly the same problem.
Yesterday i installed ubuntu server 20.04 on virtualbox - and on that i installed rocketchat via snap package (Version 3.2.2). I did so to try out the mentioned Livechat feature.
But as dkuebler describes - the Livechat can’t be found in the settings, as described in https://docs.rocket.chat/guides/administrator-guides/livechat
Settings with L that you can find on my install are:
Layout
LDAP
LiveSteam & Broadcasting
Logs
Would be great if anyone could give us a hint there.
Edit - i think i found it (still playing around with the function - not tested):
Go to Admin-> Settings-> Omnichannel
there is a Live Chat Tab there.
Also in those settings if you enable Omnichannel + save - and leave admin settings afterwards - you see that an Omnichannel option is added in the menu you used before to enter the admin settings.
Click that and you got some more Live Chat options. Those look like the settings described in the docs linked above.