Link to paper: https://thephd.dev/_vendor/future_cxx/papers/d1967.html

Quote from proposed wording:
Additionally, an array of ordinary character type may be initialized by a UTF-8 string literal, or by such a string literal enclosed in braces. Successive characters of the value of the string-literal initialize the elements of the array.

The wording does not address the case of UTF-8 code units in the value of the u8 string literal with numerical values that exceed the range of values representable by signed char.