This is a living list, gathering links suggested by the community. Please share your recommendations in the comments section or Discord, I'll update this post accordingly. Thanks!
Mirror (Docs, Pong example): Free Networking API designed to be ease of use, it reportedly has a good reputation.
Mirage: An allegedly improved fork of Mirror, with more features
Photon Bolt (Official tutorial): Offers cloud hosting for game servers, with a free plan that is more than enough for a jam game.
Article: Choosing the right netcode for your game (compares MLAPI, DarkRift 2, Photon PUN, Photon Quantum 2.0 & Mirror)