if you want a free and open online community with lots of diverse and open servers get minecraft or literally any other open world survival crafting game. this game only has passworded/closed games or a FEW whitelisted servers where you have to pass an interview with staff. this games community is made up of very introverted people who dont like strangers too much. and for some reason the devs feel like the hosts shoudnt get to decide for themselves whether they want to close their lobbies with a password or not. its silly but valheim fans will defend this practice to death. it is what it is...
maybe take a look at conan exiles. seems very similiar in some ways and there are actually open servers with lots of people. but if you dont mind the whole discord and job interview shenanigans than google some servers. there are many third party sites which list dedicated servers like https://www.battlemetrics.com/servers/valheim or the fairly unreliable https://valheimservers.net/.
i guess the upside to that isolationist multiplayer policy is that you dont have to deal with too many griefers. i still think the devs could have come up with a better solution and give hosts more freedom in how they want to host their game but the players who still play this game dont seem to mind much.