The bank only wants a notary confirmation, and a deed that the land charge was ordered by the notary (Rangattest??)
The notary confirmation is the Rangattest. The deed is the enforceable version of the land charge order – basically the document you signed during the land charge notarization.
After I found out from the tax office that they have a mountain of work (as always) and we can expect processing earliest in 4-6 weeks
4-8 weeks is normal. It has nothing to do with an unusually high workload.
that means we would have to wait comfortably another 8 weeks before we can even think about paying
It depends on what is stated in the purchase agreement. If the certificate of no objection (= certificate from the tax office that the real estate transfer tax has been paid) is not explicitly a condition, then earlier is also possible.
However, without this certificate, you will not become the owner in the land register. That is a prerequisite for the ownership transfer.
Is this correct? Or is the process nonsense
Yes, that is the completely normal process.
If you sign the purchase agreement in mid-August, I would also expect the earliest purchase price due date to be 09/30. That is a completely normal timeframe for you.