To some extent, yes, but you shouldn’t expect that it will be a huge difference.
Mastering aims only to bring the song to industry standards.
If there was no mastering engineer, then the whole industry would sound horrible. That loud, that quiet, that bright, or that dim song would be a big problem for everyone, artists and manufacturers of audio systems, and especially for listeners.
So, in the industry, there are a number of standards and unspoken rules which must be adhered to. The mastering engineers help us with that.
But do not underestimate the mastering engineer, he acts on the entire mix immediately with his actions, so this is very responsible and delicate work. Also, as a new participant in the process, he can hear certain flaws in the sound and give recommendations to a mixing engineer. This, by the way, is the main feature of the mastering engineer online mixing mastering – unlike online instant mastering services such as Landr, eMastered, etc., they cannot give you recommendations on a mix, and these services are aimed at mastering demo tracks and non-commercial projects. So for now, all commercial tracks are made by people. That can be changed in the future, but now online mastering is made by people.
Mastering Engineers have to give you a finished track. That’s called a master track.
You can ask for some special versions like MfiT or Spotify, if needed.
They differ on volume, and MfiT different codec and format. This is where the work on your song is over. Congratulations)