Maximum video and audio quality

Hello, good evening everyone, I wanted to answer a simple question that I couldn’t find on Google about MKVToolNix, when I’m mixing videos and audios in it, I leave all the side options blank, that is, I leave them all as default, I only change things like the name of the audio and of the subtitle, I wanted to know if this is ensuring that my final file has the best possible quality like the source or should I modify some items to improve, as we have many options in relation to video and audio compression and colors and sizes, thank you in advance for the answers.

MKVToolNix does not contain decoders or encoders. It cannot change the quality of the content at all. All it does happens at the container level, repackaging content from one container format to another while changing container properties.

Thanks for the answer