It does not record the steps performed in Oracle Forms 12c, as an example the username and password
NeoLoad supports Oracle Forms 12c. You said that it did not record some steps like username/password. But at least do you see Oracle forms requests in your user path or only the first HTML pages?
A pre-requisites for the Oracle forms recording is to make sure that your server is configured in servlet mode (HTTP mode) and not socket mode since this mode is not supported.
To check the Oracle forms mode use the flag request feature in your user path and search in the recorded responses (4th options) if you can find "var xconnectMode = "socket""