games listed from the wiki that i think meet dragon's requirements for cross-platform/play and that have not been answered alreadyAtomic Ninjas(PC, Xbox)
Call of Duty: Black Ops Cold War(PC, PS4, XBbox)
Chess Ultra(PC, Xbox, Switch)
Cubemen 2(PC, Mobile, Wii u)
Disc Jam(PC, PS4, Switch)
Dragon Quest X(PC, Mobile, PS4, Switch/Wii U, 3DS)
Dragon's Dogma Online(PC, PS3/4/Vita)
Dreil(PC, Wii U)
Eagle Flight(PC, PS4)
Elemental Knights R(Mobile, Switch)
Eve: Valkyire(PC, PS4)
Exorder(PC, Switch)
Fantasy Strike(PC, PS4, Switch)
Final Fantasy: Crystal Chronicles(Mobile, PS4, Switch)
Frozen Synapse(PC, Mobile)
Gears of War 4(PC, Xbox)
Gears 5(PC, Xbox)
Genesis(PC, PS4)
GROUNDED(PC, Xbox)
Hero Siege(PC, Mobile, PS4, Switch)
Hover(PC, PS4, XBOX, Switch)
Halo Wars 2(PC, Xbox)
Killer Instinct(PC, Xbox)
Minetest(PC, Mobile) not sure if this counts
Onigiri(PC, Switch)
Phantom Dust(PC, Xbox)
Pinball FX 3(PC, PS4, Xbox, Switch)
Pox Nora(PC, PS4)
Pure Chess(PC, Wii U, 3DS)
ReadySet Heroes(PC, PS4)
Riptide GP Renegade(PC, Xbox, Switch)
Roblox(PC, Mobile, Android)
Shadowverse(PC, Mobile)
Sparc(PC, PS4)
Sports Bar VR(PC, PS4)
Streets of Rage 4(PC, Xbox)
Square Heroes(PC, PS4)
Super Dungeon Bros(PC, PS4, Xbox)
Super Mega Baseball 2(PC, PS4, Xbox, Switch)
Surviv.io(PC, Mobile)
Talisman: Digital Edition(PC, Mobile, Switch)
Tetris Effect(PC, Xbox)
Tooth and Tail(PC, PS4)
Ultimate Chicken Horse(PC, PS4, Switch)
Vainglory(PC, Mobile)
War Thunder(PC, PS4, Xbox)
Warspear(PC, Mobile)
Yu-Gi-Oh! Duel Links(PC, Mobile)
Zoo Tycoon: Ultimate Animal Collection(PC, Xbox)