foo1.cs

if (arguments[currentIndex].MatchingParameter?.Element.IndexOf() is {} index && index >= 0)
// vs.
if (arguments[currentIndex].MatchingParameter?.Element.IndexOf() is >= 0 and var index)

foo2.cs

var argumentsMax = TryGetMethodArgumentAbstractValues();
if (argumentsMax == null) return null;

if (argumentsMax.Count != 2) return null;

// vs

var argumentsMax = TryGetMethodArgumentAbstractValues();
if (argumentsMax is null or { Count: not 2 }) return null;