A quick heads up.

The /etc/odoo/odoo.conf file needs to be updated if you want to have your own database in current build 18.0.

To fix:

Easiest is to Select "Database Manager" at the login screen for Odoo
Specify a new Database

login with Webmin.  Choose "Tools" / "FileManager"

navigate to /etc/odoo/odoo.conf

find the line that says 
db_name = TurnkeylinuxExample
make it read
# db_name = TurnkeylinuxExample

then

db_name = NewDatabaseName

or

db_name = 

Save the File

--

next (critical) in Webmin go to:

System  -  Bootup and Shutdown

scroll down to the "odoo.service"
select it (checkbox)

Scroll down and select RESTART  (don't have anything else selected but odoo.service when you do that

Refresh your Database or Login Screen and you should be on your way.

If you don't update the odoo.conf file you will be restricted to working with TurnkeyLinuxExample database which, imho is not the best way to approach your company data.

----
Several other modifications to your odoo.conf will need to be done to build out an optimized system, but start with this one.