"Digital" is ambiguous.
CD, DVD, Blu-Ray are digital as well and it's not immediately obvious if "Digital" also includes them. There's also that ugly format called SACD, and it's not a valid choice in the album search, so it's even less obvious if "Digital" includes SACD.
"Digital" is used for web releases here (if I got that 100% right), and one can't download from the web something that's not digital anyway.
Therefore I propose replacing "Digital" with "Web". (or "Internet" if you wish).
What are possible drawbacks?

It's "digital" as opposed to "(on a )physical( medium)", not analog. I think it's quite obvious that that's what is meant, since we have separate categories for CDs, DVDs and Blu-rays.

You can mention special formats like SACD in the version description (select "CD" as the main format, though; if it's something really exotic or unusual, use "Other").

Perhaps slightly off-topic, but *should* SACD go under the CD format? The hybrid type make sense to list as CD to me as they can be played by a CD-player, but the non-hybrid SACDs aren't actually playable on a normal CD-player...

It's still an audio compact disc, isn't it?

Fair enough. It's uncommon enough a format that I haven't had to deal with it on MA I think (or if I did, I don't remember), but seeing it mentioned had me think what it should be listed like, with CD being my first thought too but then I started doubting/overthinking it and I figured I might as well double-check.

No, "digital" in my view is definitely perfect. As Azmodes said, it's obvious that "digital" means "it's not a physical CD" or whatever, a tape, a vinyl. I mean, obvious to anyone. Special physical CDs can be specified in the notes etc.

There were quite a few metal albums released on SACD. Mostly from relatively popular bands (Manowar for example). But this is, fortunately, nothing compared to other, more sensible formats.

And yes, SACDs (unless they are hybrid) normally cannot be played neither on a CD player, nor even a computer. Accidentally buying a SACD instead of a normal CD could be a complete failure.