//my vector class
public readonly struct Vec2<TScalar>(TScalar x, TScalar y) :
    IVector<Vec2<TScalar>, TScalar>
    where TScalar : INumber<TScalar>
{ ... }

//my interface
public interface IVector<TSelf, TScalar> : IVector<TScalar>,
    IAdditiveIdentity<TSelf, TSelf>,
    IMultiplicativeIdentity<TSelf, TScalar>,
    IAdditionOperators<TSelf, TSelf, TSelf>,
    ISubtractionOperators<TSelf, TSelf, TSelf>,
    IMultiplyOperators<TSelf, TScalar, TSelf>,
    IDivisionOperators<TSelf, TScalar, TSelf>,
    IUnaryNegationOperators<TSelf, TSelf>,
    IUnaryPlusOperators<TSelf, TSelf>,
    IEqualityOperators<TSelf, TSelf, bool>,
    IEquatable<TSelf>
    where TSelf : IVector<TSelf, TScalar>
    where TScalar : INumber<TScalar>
{
    static abstract int Rank { get; }
    TScalar this[int axis] { get; }

    public static virtual TScalar Dot(TSelf a, TSelf b)
    {
        TScalar val = TScalar.Zero;
        for (int i = 0; i < TSelf.Rank; i++)
        {
            val += a[i] * b[i];
        }
        return val;
    }
}

//my extension method
public static TScalar Dot<TVec, TScalar>(this TVec a, TVec b)
    where TVec : IVector<TVec, TScalar>
    where TScalar : INumber<TScalar>
{
    return TVec.Dot(a, b);
}

//my test code
Vec2<float> a = new(1, 2);
var x = a.Dot(a);//error here, said cs0411: The type arguments for method 'method' cannot be inferred from the usage

//my vector class
public readonly struct Vec2<TScalar>(TScalar x, TScalar y) :
    IVector<Vec2<TScalar>, TScalar>
    where TScalar : INumber<TScalar>
{ ... }

//my interface
public interface IVector<TSelf, TScalar> : IVector<TScalar>,
    IAdditiveIdentity<TSelf, TSelf>,
    IMultiplicativeIdentity<TSelf, TScalar>,
    IAdditionOperators<TSelf, TSelf, TSelf>,
    ISubtractionOperators<TSelf, TSelf, TSelf>,
    IMultiplyOperators<TSelf, TScalar, TSelf>,
    IDivisionOperators<TSelf, TScalar, TSelf>,
    IUnaryNegationOperators<TSelf, TSelf>,
    IUnaryPlusOperators<TSelf, TSelf>,
    IEqualityOperators<TSelf, TSelf, bool>,
    IEquatable<TSelf>
    where TSelf : IVector<TSelf, TScalar>
    where TScalar : INumber<TScalar>
{
    static abstract int Rank { get; }
    TScalar this[int axis] { get; }

    public static virtual TScalar Dot(TSelf a, TSelf b)
    {
        TScalar val = TScalar.Zero;
        for (int i = 0; i < TSelf.Rank; i++)
        {
            val += a[i] * b[i];
        }
        return val;
    }
}

//my extension method
public static TScalar Dot<TVec, TScalar>(this TVec a, TVec b)
    where TVec : IVector<TVec, TScalar>
    where TScalar : INumber<TScalar>
{
    return TVec.Dot(a, b);
}

//my test code
Vec2<float> a = new(1, 2);
var x = a.Dot(a);//error here, said cs0411: The type arguments for method 'method' cannot be inferred from the usage