ora-12560: tns:protocol adapter error

The Oracle 18 XE installation creates a windows service called OracleServiceXE.

I'm not sure of what your problem is, I understand that you had 11g installed (XE or SE or EE?) and you uninstalled it to install 18c XE (that is OK if the 11g was also a XE edition, you can only have one XE installed on the same machine).

Did the 18c XE installation finished OK? If not, do you want to fix the 18c installation or do you want to reinstall the 11g?

Please explain with more details what you have done, the problems you have and include the exact syntax and errors. Use some screen capture (if you are using a GUI tool) or directly copy/paste if you are using command line.

And also please follow this guideline when posting new questions, that will help you get answers quicker:

https://community.oracle.com/message/9362002#

Let's start from the beggining

1) Check the SERVICES app and verify that you have both the OracleServiceXE and the Listener installed and Running :

2) Go to a command windows, execute the following to check if the database is registered with the Listener

lsnrctl status

lsnrctl services

3) Try connecting using SQL*Plus and local connection

SET ORACLE_SID=XE

sqlplus / as sysdba

Show us the results so we can check what the problem is...

1) You do not have an OracleServiceXE, that means that something on the 18c XE installation went wrong.

2) You have 2 listeners (11g and 18c). That should not be a problem, unless they try to run on the same port. From the screenshot, the 18c listener seems to run on the 1522 port so that seems to be OK (default 1521 port must be in use by 11g listener). Both of them are down, that's why you do not see results on the lsnrctl commands. The 11g listener seems to be on a "Client" home, that is weird AFAIK...

3) If the service does not exists (problem #1) it is imposible to connect to the DB, so it is obvious that sqlplus will fail.

I would suggest you to uninstall everything (both failed 18c XE and existing 11g components) and run the 18c XE installation again. Please follow the instructions with all the details. Make sure that ORACLE_HOME and any other environment settings are configured before starting the installation.

If you do not have OracleServiceXE as a service, and started, that means you do not have the XE database created.

The initial post seemed to be pointing to a connection error (you mentioned that XE installation was OK) but the absence of the service means the installation did not end OK. Maybe someone from Oracle in the forum can guide you to complete the installation, you can search other questions in this space where there are detailed explanation on how to make a complete uninstall and a new install of OracleXE.

Check the O.S version and edition, the required privileges, etc etc etc.