Can you give me some advice on a TV series?

It’s the 20 episodes or more that’s tough. Only comedies really have that.
If it floats your boat, Netflix’s Marvel series are good. Jessica Jones, Daredevil, Luke Cage, Iron fist and Defenders. That should keep you busy.

Won’t find much sci-fi, action, adventure series’ with that many episodes a season. Like @Rarebear said, that’s usually the domain of comedies. Sitcoms, which can be shot in studio, typically with no more than a handful of sets that remain, more or less, the same over the life of the series, are cheap and easy to produce. Those other genres are often shot on location and/or have a lot of effects that quickly add up to a lot of expense. That’s why most non-sitcoms typically have 13 or less episodes a season.

As @Rarebear wrote, not with 20+ per season. Without that restriction some that come to mind include:
The Expanse
Rake
Better Call Saul
The Last Kingdom
House of Cards
Stranger Things
The Goodwife
The OA
Sneaky Pete.

Sherlock comes to mind, but there are only about 4 episodes per season.

Merlin is lightweight fare, kind of cute.