So this is a conscious design decision from our side so that it doesn't get missed from the user. What you can do is something like:

ts
let connectionURI: string | undefined = process.env.SUPERTOKENS_URI;

if (connectionURI === undefined) {
  throw new Error("Please provide the SuperTokens connectionURI");
}

supertokens.init({...})

This way, I think TS will stop throwing the error.