Hi! I used a service called Hathora (https://hathora.dev/) to manage my servers. It's not so different then what you found on tutorials. Essentially, instead of you clicking "host" on the game in your PC, Hathora will spin the server for you, and then the client can connect to it. The server rooms are also populated by Hathora, so you can just request for it and show in your game. I recommend entering their Discord Server, so they can help you out. Other way of doing it is getting a Server in AWS, Azure, DigitalOcean etc and spinning up the server yourself, although this will be harder if you never did it before. Good luck =)
I didn't use Hathora on Brave Hamlet Online, as Hathora is best for match-based games (when you have a room, everybody enters, plays and eventually it's over). Brave Hamlet Online was a 24/7 MMORPG game with a single server, so I spinned up a server inside a Digital Ocean VPS (that costed $48/month, although for a small game like that I probably could have used a $12/month, but I just didn't have the time to test it). Hathora is not free, but you gain $200 when you sign in to test the service. After that, you are charged for how much time a server was running (so this means that if no one plays your game, you are charged nothing). For a match-based game, I think it's very worth it.
A Digital Ocean VPS (https://www.digitalocean.com/), as I said in the comment. Only that and Nakama, to be fair. The rest was all the server made in Godot.
About the authentication in Brave Hamlet Online, we used a opensource pre-built game server called Nakama (https://heroiclabs.com/nakama/). Nakama took care of auth and saving the players inventory and money. All the rest was our server made in Godot