That error looks like the type that you get when your numbers variable is not actually typed as an Array.

For example, if you have some code where the numbers variable was an object or an integer or a string:

var numbers ="1,6,3";
numbers.sort((a,b) => a - b);

You will get Uncaught TypeError: numbers.sort is not a function because there is no sort function for strings.

But if you check this exact snippet of code:

var numbers = [3,6,1];
numbers.sort((a,b) => a - b);

You should definitely not see any errors.

When you say:

VS Code does not recognize the method

This makes me think you are seeing IDE debugging warnings which could also be due to other problems with the your VS Code and extensions config.

But my first recommendation on debugging would be to check the TYPE of the numbers variable just before you call numbers.sort() and confirm that it is an Array