After you upgrade to Oracle Database 23ai, you can install patches either as gold images or individual software patches by downloading the patches from My Oracle Support.

• About Oracle Database Release Update Patches
  Oracle provides quarterly updates in the form of Release Updates (RUs) to release new features, upgrade existing features, enhance security, or fix problems with supported software.
• Downloading Release Update Patches
  Download and install Release Updates (RU) and Monthly Recommended Patches (MRPs) patches for your Oracle software after you complete your installation.
• Applying Out-of-Place Oracle Database Patches
  Use this procedure on the local cluster node to perform out-of-place patching of Oracle Real Application Clusters (Oracle RAC) database.
• Patching Oracle Database Using Oracle FPP Local Mode
  Use this procedure to patch Oracle Database using Oracle Fleet Patching and Provisioning (Oracle FPP) Local Mode.