What is the best way to archive an old user in G Suite? 

Leaving mailboxes and Google Drive accounts of former employees active on Google Workspace is a common practice, but it results in unnecessary costs. Also, backing up their data after they leave may be too late.

69% CIOs fear data loss when employees leave – Osterman research

The best approach to protect the data assets of ex-employees is to automatically archive their emails and files to an independent cloud archive like Vaultastic, from the day they joined (and not after they leave). By doing so, you ensure that the data is securely stored in a centralized location, providing better control, redundancy, and long-term protection without the ongoing costs of maintaining inactive accounts. And without the risks of accidental or intentional erasure of the information.