Unexpected token '?' discord.js

That ?? is the nullish coalescing operator. Your error means you're running a version of node.js that does not support it. You'll want to upgrade to at least node version 14 to access this feature. Unfortunately, repl.it does not support upgrading to a newer version unless there is already a version for it when creating the repo.

To use the latest version of the DiscordJS library you will actually need Node v16+.

I tried to run a server application instance on Vercel that used DiscordJS but it uses Node version 14.x runtime. This ended up as an error and you need to use/host your server in an environment that is Node version 16.x+.