> 1e97 mod 97
[...]
> My much more modern calculator of a different brand also gets it wrong.)
The Windows (8.1, 10) calculator app produces 10. This is also the case with the stock calculator app on a Windows phone I bought a couple of years ago for less than USD 200. The Windows calculator is actually an amazingly good job, despite its drab appearances [1].
The stock PowerShell interpreters on those Windows systems and Python 3.6.5, all produce 3, even though I tried to convince them to use their big int facilities. But I am not too fluent with those, so perhaps that can still be done.
The stock claculator app on a a recent iPhone that costs more than any piece of hardware mentioned above does not have the Mod operator in its advanced mode :) That was also the case with the most popular calculator app I tried in AppStore. I have not tried more of them.
Cheers,
V.
