Proposed resolution (approved by CWG 2023-12-01):

Change in 6.8.2 [basic.fundamental] paragraph 15 as follows:

The types denoted by cv std::nullptr_t are distinct types. A value of type std::nullptr_t is a null pointer constant (7.3.12 [conv.ptr]). Such values participate in the pointer and the pointer-to-member conversions (7.3.12 [conv.ptr], 7.3.13 [conv.mem]). sizeof(std::nullptr_t) shall be equal to sizeof(void*).

The types described in this subclause are called fundamental types. [Note 11: Even if the implementation defines two or more fundamental types to have the same value representation, they are nevertheless different types. —end note]

It is unclear whether cv std::nullptr_t is a fundamental type, given that it is declared in a library header and cv-qualifications are not mentioned in 6.8.2 [basic.fundamental] paragraph 15.