Welcome to the Make community!
You can list/search all files in the folder. This will output one bundle per file.
Then,
When you have multiple bundles and want just one item, you can use an Array Aggregator first to combine them into an array, then use the shuffle-first functions.
If you already have an array, then just use the shuffle-first functions directly. You can put this in a Set Variable module if you need a module to put these functions in.
{{ first(shuffle(array)) }}
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!