Can't find missing packages Oracle Linux 8
You want to install the &quot;oracle-database-preinstall-18c&quot; package, using the &quot;yum&quot; utility as root. That will load all of your dependencies for you:
[root@orcl1 ~]# yum search oracle-database-preinstall-18c
Loaded plugins: langpacks, ulninfo
================================================================== N/S matched: oracle-database-preinstall-18c ===================================================================
oracle-database-preinstall-18c.x86_64 : Sets the system for Oracle Database single instance and Real Application Cluster install for Oracle Linux 7

[root@orcl1 ~]# yum install oracle-database-preinstall-18c
Resolving Dependencies
--&gt; Running transaction check
---&gt; Package oracle-database-preinstall-18c.x86_64 0:1.0-1.el7 will be installed
--&gt; Processing Dependency: compat-libstdc++-33 for package: oracle-database-preinstall-18c-1.0-1.el7.x86_64
--&gt; Running transaction check
---&gt; Package compat-libstdc++-33.x86_64 0:3.2.3-72.el7 will be installed
--&gt; Finished Dependency Resolution

Dependencies Resolved

==================================================================================================================================================================================
 Package                                                   Arch                              Version                                  Repository                             Size
==================================================================================================================================================================================
Installing:
 oracle-database-preinstall-18c                            x86_64                            1.0-1.el7                                ol7_latest                             18 k
Installing for dependencies:
 compat-libstdc++-33                                       x86_64                            3.2.3-72.el7                             ol7_latest                            190 k

Transaction Summary
==================================================================================================================================================================================
Install  1 Package (+1 Dependent package)

Total download size: 208 k
Installed size: 866 k
Is this ok [y/d/N]:

It should be noted that Oracle 18c isn't supported on Oracle Linux 8; ideally you should be using Oracle Linux 7. See these articles for install steps and guidelines:

Database Installation Guide for Linux
Oracle Database 18c Installation On Oracle Linux 8 (OL8)