There's enet (https://github.com/lsalzman/enet) or something like naia (https://github.com/naia-lib/naia) which supposedly uses ideas from the old (but very reliable back in the day) networking of the game Tribes 2 (https://github.com/nardo/tnl2 / https://www.gamedevs.org/uploads/tribes-networking-model.pdf).