Firefox

peer 2 peer, but you still need "router"/relays in order to do that. Your data still need to move via public server, called relays, I will call that router, because it's not 100% p2p, because there are other protocol that can be more lower p2p, using udp punch hole. And don't need any relays, and will work even behind firewall, as allowed to open connection outside, and going back using that punch hole.

I'm a prominent community donator via my company and personal server in 2018-2019 (not bragging, but it's), for asia pasific https://relays.syncthing.net/ At that time I choose to stop, because too much user, and some quite abusive with the traffic (we can't choose to drop abusive user, so yeah)

I seen nowdays that the server relay grown, it's good, but still, you need more relays to balance the network. Anyway, syncthing isn't for me, because I don't have 24 hours a day in my house running my computer in order to check my data. or I will use Synology/FreeNAS with ZeroTier, to achieve real P2P, well, P2P in term of network, data in NAS.