Hello! I need to pad a number on the left, which is easy
 with nf, but I also want commas such as nfc! However, nfc
 only can pad right! Why is this/can someone help me make a workaround?

I tried this code:

int longNumber = 1000 //big number
String longNumberO= nf(longNumber, 10); //big number with 10 zeros in front
String longNumberOC = nfc(longNumberO); //big number with 10 zeros in front and commas

but I get the error: "The method nfc(int[]) in the type PApplet
is not applicable for the arguments (String)"

reference
Syntax

nf(intValue, digits)
nf(floatValue, left, right)

nfc(intValue)
nfc(floatValue, right)