Consider this invalid conversion for this generic-lambda to pointer to function which is defined by "decltype(+[](T&& t )->T{return t+1;}".
This ICE happens when original accepted parameter type changed from "T" to "T&&".
See compiler explorer (https://www.godbolt.org/z/fde1bc3zE)

I suspect this is some related issue with another unconfirmed case PR104358.

template<typename T>
auto foo(T&& t, decltype(+[](T&& t )->T{return t+1;}) lam){
	return lam(t);
}
void test(){
	foo<int>(5, [](int t){return t+1;});
}


<source>:8:21: error: invalid user-defined conversion from 'test()::<lambda(int)>' to 'int (*)(int&&)' [-fpermissive]
    8 |         foo<int>(5, [](int t){return t+1;});
      |                     ^~~~~~~~~~~~~~~~~~~~~~
...
internal compiler error: error reporting routines re-entered.
0x2174365 warning_at(unsigned int, int, char const*, ...)
...