How to multiply a float4x4 and a float4 in unity shaders?

I'm trying to make a post-processing shader to simulate what a colorblind person would see. In glsl you should just need to multiply the color by a mat4 but unity shaders doesn't have this since I think it uses hlsl. I've been trying to figure out how to do it in Unity Shaders but can't figure it out. Right now the error I get is "type mismatch" on line 55 which is (float4 col = tex2D(_MainTex, i.uv);) Does anyone know how to do this? Thanks in advance.

                 sampler2D _MainTex;
                 float4x4 _Tritanopia = {
                     0.97, 0.11, -0.08, 0.0,
                     0.02, 0.82, 0.16, 0.0,
                     -0.06, 0.88, 0.18, 0.0,
                     0.0, 0.0, 0.0, 1.0
                 };
     
                 float4 frag (v2f i) : SV_Target
                 {
                     float4 col = tex2D(_MainTex, i.uv);
                     // just invert the colors
                     col = col * _Tritanopia;
                     return col;
                 }
                 ENDCG