So the correct behavior indeed is to map to U+13DD and this looks like a bug.
FYI: the reason why it folds to the uppercase form is to have consistent behavior with older versions of Unicode. Cherokee originally only had its uppercase letters present in Unicode and only became a bicameral script in 8.0.0.
@mpvl , you're referencing the v14 tables on purpose? The Unicode v14 tables do have different case fold mappings than v13. It looks like x/text/cases is using Unicode v14 tables even though it claims to be Unicode version 13. That's possibly the culprit. The example in #47755 shows a few other characters that have this struggle.