Version Used: main branch

Steps to Reproduce:

using System.Collections;
using System.Collections.Generic;

BadCandidateForCollectionExpression xs = [123]; // no .Add(int)
BadCandidateForCollectionExpression ys = ["abc"]; // not int element type
BadCandidateForCollectionExpression zs = [default]; // ????

class BadCandidateForCollectionExpression : IEnumerable<int>
{
  public void Add(string s) { }

  IEnumerator<int> IEnumerable<int>.GetEnumerator() { yield break; }
  IEnumerator IEnumerable.GetEnumerator() { yield break; }
}

Expected Behavior:

Impossible to fill the collection expression, no Add method can accept the value of int type - the element type inferred as a collection expression element type.

Actual Behavior:

If the expression is both convertible to inferred element type and can be accepted by some non-int Add method overload - it compiles successfully.
As the result you have a really weird language context - you can only pass expressions that are implicitly convertible to int, but the invoked method accepts string value.

I guess this is the poorly written check in frontend, I guess instead of checking the element expression to be convertible to int you probably must check the parameter type of invoked .Add() method to have type convertible to int.