Apparently with the 18.104.22.168 patchset oracle imposes a new way of patching. the patches are no longer cumulative but are a complete installation.
This implies that you have to install a new home and point the old instance to the new home...
this is what oracle says about it :
"ote the following changes with the new patch set packaging:
New installations consist of installing the most recent patch set, rather than installing a base release and then upgrading to a patch release.
Direct upgrades from previous releases to the most recent patch set are supported.
Out-of-place patch set upgrades recommended, in which you install the patch set into a new, separate Oracle home. In-place upgrades are supported, but not recommended.
This feature enables you to upgrade an existing installation of Oracle database to Oracle Database 11g Release 2 (22.214.171.124) into the same Oracle home directory by replacing the existing database files. The patch set application requires more downtime and is not recommended. This upgrade type requires less disk space.
If you select In-place upgrade to upgrade Oracle database to the latest version, then you must:
Review "Optionally Performing an In-Place Upgrade (Into the Same Oracle Home)" in Oracle Database Upgrade Guide.
Take a complete backup of your Oracle home directory before you perform the upgrade.
This feature enables you to install Oracle Database 11g Release 2 (126.96.36.199) in a new, separate Oracle home directory. After the installation is complete, the data from the database in the old Oracle home directory is migrated to the database in the new Oracle home directory.
Out-of-place upgrade process is similar to Oracle database upgrade from one version to another and is the recommended type. The benefits of this upgrade type is that the patch set application requires much less downtime, and is safer when the patch set application must be aborted. This upgrade type requires more disk space to accommodate two Oracle home directories simultaneously."
I still have to test how this works but i can imagine that this can cause serious issues on space tight partitions. I don't see why they changed this way of working...