There is not a lot of difference. Some manufacturers will add materials that have certain properties, but in real-life use, those properties will be minimal.
Whitening toothpaste contains a higher level of abrasives, essentially “scrubbing” the surface of the tooth clean. This can damage enamel over time. They may also contain bleaching agents.
“Enamel repair” toothpaste contains calcium-based substances that are reputed to replace the surface layer of enamel. They are essentially a stopgap, and the material that’s deposited will be removed pretty swiftly. We cannot replace enamel manually, and the body doesn’t produce any more over time.
Cavity protection will be through addition of sodium fluoride, which is proven to help with strengthening of the enamel. So that actually does work, but the vast majority of toothpastes have sodium fluoride in them anyway, so claiming “cavity protection” is redundant.
Put simply, one should just buy a cheap, fluoride-containing toothpaste, and use it. The physical action of brushing is far, far more important than the type of paste we use.