Both shows are extremely similar.
-Both have our female lead getting back on her life after losing their status and value.

-Both Female lead divorces their husbands in the course of the show.

-Both Female lead fall in love again with a different man
QOR (2nd lead chaebol PSH, who becomes the main lead after a few episodes in the beginning) and in

20 again (her childhood friend whose first love is the main female lead, he is the main lead from the beginning).

-Both shows have great romances and comedy.

-Both main lead(PSH & LSY) are so much in love with the female lead and have great character development.

-Both husbands are very much not likable.
Husbands from 20 again is a bigger jerk.