I’ve just signed up with GA and have ordered a Smart Card. I attempted to order a DAY Travelcard and one is offered, but instructions are given for collection – not sure that even GA will put a DAY Travelcard on their Smart Card.
I have done as much research as I can and I am sure that, at present, TfL only offer a paper DAY Travelcard; it says in their website that they will cease to offer the paper DAY Travelcard in January 2023.
I get the feeling that an electronic DAY Travelcard is simply not available. Perhaps it will be after January 2023.
It is certainly the case that for Oyster, EMR, GA and doubtless others, a WEEKLY electronic Travelcard can be purchased.