Hi,
You would normally only register for VAT in the UK if you are making supplies here which are over the £85000 threshold. However, if you are a non established trader, that is, have no esablishemt in the UK then you would need to register immediately in the UK if you are making digital supplies to consumers in the UK as there would be no threshold to consider.
However, if you are making digital supplies to a UK based business from Germany then this would be accountable under the reverse charge procedure by the UK business and so there would be no requirement to register for VAT in the UK.
You can see guidance here:
Reverse charge
Working out whether you need to register
Non-established-taxable-persons (NETPs) — basic information
Thank you.