I don't think that's possible with a number field. You'd have to concatenate the fraction to the whole number in a formula field.

In my previous post I assumed you wanted to use ¼ instead of .25

geral, if you want a starting point this might help. This code goes into a formula field...

let myNum := format(Number, "#,###.##0");
let decLoc := index(myNum, ".") + 1;
let myDecimal := substr(myNum, decLoc, 3);
let myFrac := "";
switch myDecimal do
case "125":
(myFrac := "⅛")
case "25":
(myFrac := "¼")
case "375":
(myFrac := "⅜")
end;
myNum := format(Number, "#,###");
myNum + " " + myFrac

You can add more case statements to test for more decimals. "Number" is just the name of the number field I use in this example. Here are a couple of links you can check out...

https://www.alt-codes.net/fraction-symbols - For the fractions

https://ninoxdb.de/en/manual/calculations/reference-of-functions-and-language - For the Ninox language reference