I cannot say what "official policy" might be. But in my experience ...
In May 2024, my wife and I applied for UK Citizenship and arranged to attend a UKVCAS (UK Visa and Citizenship Application Service) site at the Swindon public library. (A couple of years prior we had used the same site to get renewal of our ILR visas.)
I took physical printouts of all our documentation. Only a few were the actual physical paper originals (such as the bill sent from the heating oil company). Others, such as bank statements or council tax statements, were all ones I initially received online as pdfs, or which I had previously scanned to pdf in order to get rid of the paper.
In every case, the person handling our applications, after taking our biometrics (photo, fingerprints), took my stack of documents and ran them through the scanner to be included when sending our applications onwards. Not once did she comment/ask about originals vs printouts of digital documents.
So, obviously, the (successful) reviews of our applications were done at the government offices using non-originals. This seems to make moot the question of supplying a non-digital original or a printout of a digital original. They were all digital copies when reviewed by the government.
(Please note: I took the trouble to provide a physical piece of paper for each document. My point is that the physical pieces of paper were mostly printouts of digital documents rather than true paper originals. Are there ways of submitting digital documents in digital form? I did not ask so I don't know. My advise is to keep it simple.)
Terry
(as of today) dual UKC/USC
Please post should "your mileage differ",