Device-specific Graphics Compatibility

[Jaws]

I'm helping an author with a large back catalog from the 70s convert her out-of-print stuff to electronic formats, and I've run into a potential device-compatibility question that the collective mind here may be able to answer:

Are there compatibility problems, even for some older devices, with PNG graphics that have transparencies? And, especially, for devices in "dark mode" (consider a nicely-rendered calligraphic dropcap surrounded by a white square on a dark background...). Are those problems limited to certain file formats (.fb, for example, is a known issue)?

[Quoth]

No transparency in ebooks period. Makes no sense. There are only niche solutions and it's pointless anyway.

Dark mode is a separate issue. Some ereaders invert everything and some only the text. Really the main advantage is power saving on OLED, but it's a current fashion due to people setting brightness too high.

Drop caps reduce reader comprehension and compatibility. They often look rubbish on ebooks even when working. Only consider Dropcaps (especially if an image) for "Print Replica" (i.e. PDF or similar that only work on big screens).

Decent ebooks are reflowable and work perfectly with screen readers / Text to speech.

Almost everything is epub. Amazon Kindles don't use epub, but the upload to publish via Amazon is best as reflowable epub. Over 92% of English Language world-wide.

Google ebooks on Playstore is best with reflowable epub upload.

Almost everything else can be distributed via Draft2Digital (reflowable epub upload); they send on to Barnes & Noble (Nook), Amazon (Kindle, Apps and Fire), Apple, Kobo and Libraries etc.

[Jaws]

Not what I was asking.

I asked about actual compatibility issues with graphics, and used an example of a common one so that people would understand why not having a transparent background might cause other problems. I really don't care if someone else thinks it's a good idea or not (and especially not for bringing books back into print). Because — as my descriptor notes — I'm aggressively device independent, I don't have access to many types of devices and can't test the way they handle graphics. I'm merely trying not to introduce an incompatibiity for devices that I don't have and can't test myself.

So, to repeat the actual question:

Do transparencies in PNG graphics — for those readers that support PNG graphics in the epub format — cause actual compatibility issues with those readers? Aesthetic preferences be damned.

[DNSB]

The only issue I’ve noticed with transparency is using dark mode where the image is not inverted so you end up with a black on black image.