I think that, beyond generally eating healthy foods, the impact of diet is largely dependent upon genetics. I’m a naturally small, lean guy. I’m not personally concerned with fat:carb:protein ratios. If I were to try to gain weight, I would probably just eat more food with a focus on high quality proteins.
As for supplements, I sometimes have hemp protein, and I think vitamin k2 and hyaluronic acid supplements are probably helpful for bone and joint strength, long term. But yeah you don’t really need anything (except arguably a k2 supplement, as it is rare in practical dietary sources).