Even in a serverless environment it can be beneficial to still store your tokens in a db that your apps need to fetch from when run if you ever want your app to scale.
There’s a maximum number of 25 app access tokens, after which when you create more it’ll kill the first ones, so in a serverless app if there’s any concurrency it can’t scale beyond 25 instances, where as if for example you’re use AWS Lambda for your serverless apps, you can simply pull the token from a DynamoDB table which will have minimal delay and allow the serverless process to grow in concurrency/complexity.