AIX v7.3 is fully supported by SAP!
After AIX 7.3 became generally available in December 2021, SAP started their validation tests on AIX 7.3. Testing went very smoothly and SAP did not encounter any AIX-related problems.
As of April 1th. 2022, AIX 7.3 is fully supported by SAP. Customers who want to exploit new AIX features in their SAP landscape (see What’s new in AIX 7.3) can now go forward.