Personally I love Counter-Strike 2 or Rocket League, both have the simplest way to play competitively - You simply play Comp and then get ranked.

Cs2 you could use Faceit or Leetify to create a team and join tournaments, though I think some cost money with a prize pool.

RL is awesome though, you get like 5 - 6 mini tournaments a day hosted by RL themselves. Similar to CS2 you get ranked and then join a tourney with skill-alike players. Very fun, very easy to set down, always feel like you can play “competitively” no matter the time available or skill.

Both games have a very quick learning curve, and then as you play and practice you slowly get better (hopefully)