A port of a freemium phone game, Pool Blitz is decent pool for free. Beware that it's got lootboxes & upgrades and stuff, but for most people, it'll be a fine 'kill time and sink balls' game. There is crossplay. Every Xbox user i've played against has been pretty low level. I've only seen one or two other platform users. Also, if the game takes more than a few seconds to find a player it will just put you against a bot that will be really really bad at the game.
On the achievement side of things, I earned most stuff organically and then farmed the 10 winstreak achievement with my phone as player 2. The other half of the achievements are going to be really time consuming and grindy, though, so if you're going for completions, your time is prolly better spent elsewhere.
2.5