Proposed resolution:

This wording is relative to N5054.

1. Modify [reverse.iterator] as indicated:

   […]
       constexpr reverse_iterator& operator++();
       constexpr reverse_iterator  operator++(int) = default;
       constexpr reverse_iterator& operator--();
       constexpr reverse_iterator  operator--(int) = default;
   […]
   

2. Modify [reverse.iter.nav] as indicated:

   […]

   constexpr reverse_iterator operator++(int);
   

   -5- Effects: As if by:

   reverse_iterator tmp = *this;
   --current;
   return tmp;
   

   […]

   constexpr reverse_iterator operator--(int);
   

   -8- Effects: As if by:

   reverse_iterator tmp = *this;
   ++current;
   return tmp;
   

   […]

3. Modify [simd.iterator] as indicated:

   […]
       constexpr simd-iterator& operator++();
       constexpr simd-iterator operator++(int) = default;
       constexpr simd-iterator& operator--();
       constexpr simd-iterator operator--(int) = default;
       constexpr reverse_iterator& operator++();
   […]
   

   […]

   constexpr simd-iterator operator++(int);
   

   -5- Effects: Equivalent to:

   simd-iterator tmp = *this;
   *this += 1;
   return tmp;
   

   […]

   constexpr simd-iterator operator--(int);
   

   -7- Effects: Equivalent to:

   simd-iterator tmp = *this;
   *this -= 1;
   return tmp;
   

   […]

Due to P3668R4, postfix forms of `operator++` and `operator--` can be defaulted since C++29. And P3785R1 made most of such default-able operators defaulted.

However, there're currently still a few default-able operators that are not defaulted, namely those of `reverse_iterator` and `simd-iterator`.