Vailias’ response makes sense.
You should definitely see a change in the viewport when toggling srgb on/off for a texture but you may have to recompile the material to see it. The same thing happens when you change to NearestNeighbor filtering. It wasn’t always like that. When I just tested it I did not have to recompile; it updated instantly but it could have changed due to engine version.
If you are ever in doubt, I would recommend using the “Debug Scalar Values” function and import a 50% grey texture. That means fill with 127 in photoshop. With srgb gamma, that 0.5 value will be remapped to ~0.21 (which is close to 0.5 ^ 2.2 which is the legacy srgb curve). But if you set sgrb to false, the texture will read exactly 0.5 again.