Ask HN: How to test data generation for complex B2B SaaS?

Hi there, I am tasked with building an analytics stack for a B2B white-label data integration & modelling SaaS where accuracy is of very high importance.

We're looking at ca. 15 disinct sources with ca. 50-60 tables.

I am told I am unable to use production data for staging/ development purposes due to GDPR. Hearing this, I am scratching my head and looking at a mountain to climb just to get back to being able to model outside of prod.

What are your tools or experiences for building reliable dummy data at scale?