To save everyone a click:
> Personal data shall be: kept in a form which permits identification of data subjects for no longer than is necessary for the purposes for which the personal data are processed. (..)
Note that this does not say "it must be stored for a limited amount of time" - it says "no longer than necessary".
Your basic account data (such as username and password, or an email for password recovery) is still necessary to log in to the platform and make use of your purchases. As long as there is no clear indication that the user will never log in again (such as due to death, or because they explicitly deleted their account), it would be reasonable to keep it around.
On the other hand, it may make sense to delete some data. For example, it may make sense to store your full name and address info to make checkout more convenient. If a user hasn't bought stuff in a while, it makes sense to delete it and have them re-enter it in the future.
There might be a bit of a gray space for things like game achievements (especially when there's a public profile) or savefile backups, but reading it as "you MUST delete all digital purchases because GDPR" is just not true.