New to Minecraft. Which version should I get for my kid?

Missed the Minecraft craze growing up as a kid myself, never played, so I'm a complete noob here. My kid is 6 and wants to play as this as his first real game, and I'm getting conflicting information about which version I should get. I'm a PC gamer (mostly steam) and homelabber, whole house runs on Debian Linux including both his PC, my PC, NAS, and other servers I have going. Planning on spinning up and hosting a server just for my kid, myself, and other family members to play on. Don't plan on running mods anytime soon, but can't rule it out entirely for down the road. Which version should I pick up (with primary concern being linux compatibility)? Will I need to buy multiple licenses for us both to be able to play concurrently? Any other recommendations you have as far as settings and setup configuration?

Thanks in advance for helping a dad out!