How to build an Jsonata for this switch node?

[greengolfer]

As @Colin said, regex is your "friend". Kind of... as it is not the friendliest stuff to use.
However if you want to send 3 and 4 to the same output, you can do:

If you want to experiment with regex, you can go to https://regex101.com/ it will help you to build the expression.

^ is beginning of string
$ is end of string
| is "or"