In the example given[1] the fields look like they are disabled. I probably wouldn't even try to type into them, I'd just assume that something was broken.
I've seen tons of disabled input fields that look like this (e.g. showing you your un-changeable email address), so yeah - that would be my first instinct as well.
The colored background container is totally fine tho, those are everywhere and they help draw attention.
Normally I'm of the opinion that, if even just one or two people have the same problem with a UI, it's probably worth considering a valid, addressable problem, no matter how much it seems like the user's "fault", but even I'm having trouble rationalizing this one. May I suggest that maybe you're having this thought because, intellectually, you know how disabled fields are frequently styled, however, in natural conditions, you probably wouldn't actually make that assumption unless not all of the fields were styled that way?
I'm familiar with them, sure. But to assume something like this is broken rather than simply a color choice would, to me, be a strange and usually wrong assumption. Given that we've all (well, most of us) been on the web for 20-some years now, and noticed that web designers, for better or worse, often stray from defaults and choose different colors.
More often than they put a form field with all the fields disabled.
I'd certainly try typing into it before I emailed customer support.
Incidently, on that codepen, the background colors of the disabled and non-disabled elements are identical, to my eyes. The only difference is in the border color. (and the behavior when clicked on)
FWIW, on my uncustomized chrome, I'm seeing the same style as FF. If I recall correctly, these have been the default styles in every browser I've seen since Netscape Navigator. Not sure about Safari.
[1]: https://uxmovement.com/wp-content/uploads/2020/01/off-white-...