Update your version of Node, it’s older than that syntax and it doesn’t support it (you will be able to turn it on via a flag when you start Node with your current version, but it’s easier long run to upgrade)
Ah. You can’t change the node version easily (there are ways to do it, but they’re not particularly friendly).
Answer is don’t use the nullish coalescing operator, it’s only saving you a line of code.
The version of Node on Replit doesn’t support it without passing flags to Node when it starts, and afaik you can’t do that. It’s 100× easier to just not use the feature you’re trying to use there.