C++20 : Making reverse iterator from custom iterator fails - c++

Question

I'm making a reverse iterator from my custom iterator on my B-Tree implementation, but it fails to work.
Full code : https://wandbox.org/permlink/hrM32RYb6oVHDHAm
My iterator implementation:
class BTreeIterator {
using difference_type = std::ptrdiff_t;
using value_type = T;
using pointer = T*;
using reference = T&;
using iterator_category = std::bidirectional_iterator_tag;
Node* node;
std::vector<T>::iterator it;
void Increment() {
// ...
}
void Decrement() {
// ...
}
public:
BTreeIterator(Node* node, std::size_t i) : node {node} {
assert(node && i <= node->key.size());
it = node->key.begin() + i;
}
reference operator*() const {
return *it;
}
pointer operator->() const {
return it;
}
BTreeIterator& operator++() {
Increment();
return *this;
}
BTreeIterator operator++(int) {
BTreeIterator temp = *this;
Increment();
return temp;
}
BTreeIterator& operator--() {
Decrement();
return *this;
}
BTreeIterator operator--(int) {
BTreeIterator temp = *this;
Decrement();
return temp;
}
friend bool operator==(const BTreeIterator& x, const BTreeIterator& y) {
return x.node == y.node && x.it == y.it;
}
friend bool operator!=(const BTreeIterator& x, const BTreeIterator& y) {
return !(x == y);
}
};
My typedef declaration in class BTree:
using iterator = BTreeIterator;
using const_iterator = BTreeConstIterator;
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
iterator begin_;
const_iterator cbegin_;
iterator end_;
const_iterator cend_;
// ...
reverse_iterator rbegin() {
return reverse_iterator(end_);
}
const_reverse_iterator rbegin() const {
return const_reverse_iterator(cend_);
}
const_reverse_iterator crbegin() const {
return const_reverse_iterator(cend_);
}
reverse_iterator rend() {
return reverse_iterator(begin_);
}
const_reverse_iterator rend() const {
return const_reverse_iterator(cbegin_);
}
const_reverse_iterator crend() const {
return const_reverse_iterator(cbegin_);
}
The compiler complains for this reason:
error: return-statement with a value, in function returning 'std::reverse_iterator<BTree<int, 2>::BTreeConstIterator>::reference' {aka 'void'}
The standard gives (https://en.cppreference.com/w/cpp/iterator/reverse_iterator):
Until C++20, std::reverse_iterator<Iter>::reference had been equal to std::iterator_traits<Iter>::reference (In my case, T&)
Since C++20, std::reverse_iterator<Iter>::reference has been changed to
std::iter_reference_t<Iter> = decltype(*std::declval<Iter&>())
It seems to became void in my case, causing the error.
My questions:
What is the rationale behind changing a reference type of a derived reverse iterator?
Why my BTreeIterator type is not referenceable? decltype(*std::declval<BTreeIterator&>()) gives void. How can I change it to T&?