A comment, not a question.
The 2020/21 API with HMRC is now open on the tax return software I use, and SEISS is a new element. Of course it shows no data yet in true HMRC style.
SEISS data is cut and dried. They know exactly what they have paid to each person. What possible reason is there for this not to be available.
The employment data should be always available too. What's the point of RTI if HMRC need months to "reconcile" it?
If they can't get these basic systems working, how can they expect to run a whole new tax reporting system?