When you see two names joined in a title, read the small word between them as information, not decoration. It says that more than one party is involved, and it hints at how. Take "Act A x Act B". That pattern usually points to a pairing presented together, with the title treating both names as the credited front. The x is a joiner, not a mathematical sign, and it is also used for pairings between an act and a non-music partner such as a brand or a product. So the x alone does not tell you which kind of pairing it is. The surrounding text does.
Now compare "Song (feat. Act B)". Here the first name is the song's owner, and the guest is credited as a feature, so feat. tells you whose release it is and who joined it. The word "with" is used more loosely. It often marks a partnership on a single song or a segment, and where it sits in the title can change what it modifies. A name placed before the song name and a name placed after it may be describing different things, so read the description before deciding what the word is attached to.
The ampersand is a different case. Between two names, an ampersand is usually a duo, or a group whose name contains an ampersand, and that is not a collaboration at all. Check whether the two names are separate acts or one act's name, because a name written with an ampersand can be a single group. Then there is the non-music partner. A description may name a brand, a game or an event in a copyright line or a one-sentence note. That tells you the partner exists and is credited. It does not tell you the terms, and a copyright line is a credit rather than an explanation of the relationship.
Where does the rest of the credit live? The title carries the main collaborators, and the description carries everything else, including any partner line and the credit block for who composed and wrote. Remix credits, cover and original-song credits, the music credit block and language versions each have their own guides. One honest limit: these labels are written differently from release to release, and a label alone does not tell you who did how much. A title names the parties and the joining word. It does not measure anyone's share.