Just going through the Mandarin onboarding in Duolingo again, and one of the common errors is that 得 is pronounced de2 in sentences where it should be dei3.
There are also common words like 星期 where the characters are the same in SC/TC, but the tone would be different in a hypothetic Duolingo TC class (xing1qi1 vs xing1qi2), and I don't recall ever hearing "下星期" in Taiwan, it was usually 下禮拜. Erhua such as "小一點兒" is also not something that feels natural in TC.
But I think you are specifically asking about characters where the mapping from SC to TC is not 1:1. This StackOverflow answer has a few examples and a link to an exhaustive list on Wikipedia: https://chinese.stackexchange.com/a/38707
I sometimes read TC clickbait articles, and when they use 后 where it should be 後 that's usually a sign of a crappy machine conversion from SC. 發髮 and 干乾幹 are two more really common character groups that map to a single SC character.
The rabbit hole goes even deeper because the same Unicode character can have typographic differences by region. Just today I learned that Apple's PingFang SC and PingFang TC fonts use a different "roof" on the character 龜, even though it is the same traditional character in both cases. More examples here: https://en.wikipedia.org/wiki/Variant_Chinese_character (but that wouldn't be an issue for a TC Duolingo class)