Is there any type of reason you would like to install the version 18? As per https://docs.oracle.com/en/java/javase/index.html the latest version is the 23.

You can download the latester version at: https://www.oracle.com/java/technologies/downloads/

You need to make sure that there is no other version of jdk installed on the computer, if you have other version that might be the reason you can not install it.

If it is your first time and you are sure you do not have another version, and you really need version 18, follow the steps at: https://docs.oracle.com/en/java/javase/18/install/installation-jdk-macos.html#GUID-C5F0BF25-3487-4F33-9275-7000C8E1C58C

If you followed it and still encounter issues, replicate Java error:JDK 17.0.1 can’t be installed on this computer response.