Gaming

Sea of thieves is great, but only plays 4 at any given time. It also has alcohol and some T rated violence, but it depends on what your boundaries are for the kids.

Minecraft

My brother and I started playing Grounded together as a way to just chill and catch up throughout the week. We were shocked with how much content was actually in the game. It’s like Valheim mixed with Honey I Shrunk The Kids, 4 player online coop, base building, survival. It has a storyline so there’s always a sense of direction and it syncs the world with everyone regardless of who plays so it’s easy to just come and go. I could definitely see a group of 10 year olds getting sucked into this.

No Man's Sky?

Space engineers. Great game for cooperation amd if they work well enough they can get a working spaceship going together and explore the universe.

The answer is whatever his friends are playing.

It would be helpful to understand what types of games the kid was playing in the first place to suggest alternatives. I ripped this answer from quora on how to see which games within roblox your child was playing

• Game History: Roblox used to have a "Game History" feature that allowed users to view a list of recently played games. This feature showed the last few games you played, but it was limited in terms of historical data. It's worth checking if this feature is still available in your account settings.
• Roblox Account Activity: You can check your Roblox account's activity feed, which may show some information about recent game interactions and achievements. However, this feed typically doesn't display a comprehensive game history.
• Roblox API: Some third-party websites and tools may offer services that attempt to retrieve and display more extensive game history data by accessing Roblox's API. Be cautious when using third-party services and make sure they are reputable and secure.

I went looking for any kind of account tracker and to no one's surprise they are mostly about account value from items, not so much about worlds/experiences they have been on.

Most of the responses I've seen on here are just suggesting games which may or may not be to your kids looking purely based on those games being generally accepted as good.

I recommend Astroneer - a solo / multiplayer survival game about collecting resources, refining stuff and building up bases on several planets. It's hecking fun in multiplayer and it doesn't have combat. There's a ton of things to do and if the kids are good at communicating with each other they can quickly conquer the game. The only microtransactiony stuff it has is cosmetics (but it's not being pushed upon you in any way), but you can unlock some of these through progression as well.

What might be a good idea is to try Game Pass for a few months and see what they settle on. Then for Birthdays or Christmas, get them the games they played the most. Not sure how parental controls are like on it, but I hope they exists.

That being said, outside of Nintendo, there aren't many Online games which don't demand their users to pay for cosmetics with fake in game currency. See CTR Nitro Fuelled, Fortnight, Call of Duty, Overwatch and Minecraft skins.

With that said if changing your system isn't an option, Minecraft Bedrock Edition the only game I am familiar with. There is a skin store, but you can't earn in game currency from just playing (from my knowledge). So if they don't have access to the credit card, they won't be tempted, plus the base game has enough options that you can customize your character well enough.

If you can get a switch (and friends have one already), Splatoon 2/3, Mario Kart 8, and Animal Crossing are all friendly non-microtransaction laden games.

I dunno if you want him playing a true mmo at that age, but old school RuneScape is currently as popular as ever. Specifically old school though, RS3 has the same sort of problems with micro transactions etc.

Microtransactions aside, if you're trying to protect your kids from creeps online you're gonna have to ban every platform that supports interactions with strangers. This includes several other games you've mentioned in the comments including Minecraft.

Personally, instead of banning it I just play it with my kids on a regular basis. There's plenty of actually decent games on Roblox and it enables game ideas that otherwise wouldn't see the light of day. My favourite is the Ikea survival game.

Games my kids enjoy without paying one cent...

All the games they play

We spend zero dollars on video games and yet our kids seem to play a lot of them, my wife and I don't really play. They even had a friend give them an Xbox and there are computers and tablets and phones in our house. Games don't have to be a money pit.

Was he interested in developing games in Roblox or just playing them? If he was interested in development, consider showing to him Godot. Do a simple tutorial together, maybe a multiplayer that he can send and show off to his friends.