I have a generic Nodemcu + Oled display which connects to my wifi fine.
I am wanting to create a script where any user can enter a wifi password via a couple of buttons without needing to touch code. I have seen system where a toggle of one button advances char through whole ascii set and other button sets and advances to next char of password, does such code exist already written?
For your particular model of oled display? Probably not. But there will probably be similar code but perhaps for other displays which could be adapted.
But entering passwords with a couple of buttons like that is a PITA. Have you had a look at the WiFi Manager library? This allows you to connect to the Arduino with a smartphone, tablet or laptop, select an SSID for the Arduino to connect to and enter the password using the smartphone/laptop screen.
EDIT: sorry, that was a very short answer! I was using the term "Arduino" in its most generic sense, ie. any MCU board that can be programmed with the Arduino IDE. But actually, WiFi Manager is only compatible with boards based on esp8266 and esp32 MCUs I think. Fortunately, NodeMCU uses an esp8266 MCU.