On the Supergirl wiki. (When that was a thing) I used to compare the similarities of the two show's first seasons. Now i'll do the same for this one.
1. We get a bit of a time skip after the last season's finale.
2. The hero gains temporary help from another superhero.
3. A friend of the hero starts his own superhero journey. He uses tech to fight crime.
4. Season 2's supervillain uses the same powers as our hero.
5. A reference to the Flash and Supergirl is put on the other character's show respectively.
6. The hero gets a new love interest for the season.
7. Season 2's supervillain kidnaps a member of the supporting cast.
8. Season 2's supervillain unleashes their army on the hero's city.
9. Our hero kisses the love interest before one of them goes into a portal.
10. The season ends on a cliffhanger.