If you need Toad 9 then installing the full 10g client should work for you if you can still find it online.

If not you might be able to use the current Toad freeware (not Trial) if it does everything you need. In addition, bugs related to client detection and establishing connections have been fixed over the years.

Toad 9 is very old and should not be expected to function with newer Oracle software. It cannot locate my 11g or 12c instant clients. My Toad 9 installation is only capable of seeing/using one of my 3 installed clients. Set TNS_ADMIN using the Environment Variables dialog in Windows. Once you close that session its value is lost. That setting is valid only for the duration of that command prompt.

When you set your TNS_ADMIN variable did you set it at the system level too? Your screenshot shows a SET TNS_ADMIN command at a command prompt. Third, Toad does not require TNS_ADMIN environment variable, but it's nice to use one especially if you have multiple clients installed and want to share your. You should be using a 10g client although an 11g client should be OK here too. Second, if you're trying to use that 12c client shown in your path you're out of luck. Toad might work with newer databases, but language syntax and data dictionary changes will cause problems for sure.

First, Toad 9 should be assumed to only work with the Oracle version that was current at the time of Toad 9 release which is 10g.

Toad for oracle trial