Extraordinary You (2019)

In both, the ML is a manga character. In EY, the story takes place within the manga, in MPBGMPB, the ML comes to the real world.

I am sure that if you liked While you were sleeping you will love Extraordinary you.
Both have a love triangle in which the woman discovers first somthing fantastic that later she shares with the men: In While you were sleeping the demale lead can see the future and later the male leads too and in Extraordinary you the female discovers that she is a Manga character and later the male lead also thanks to her and also in both dramas the three main characters look for solutions to the problem and try tu change their fate.

I'am not good at explaining myself but I swear that you will not regret watching the drama.

The two are high school romance dramas with love triangle and cute female leads ,tall and handsome male leads and pretty love stories .

both have "things not everyone can see" vibe going on, as in the hotel with the ghosts for Hotel Del Luna and the realization of the life outside the comic in Extraordinary You
the link to the past ("past" in EY case being previous story)

and similar ending

They both have high school settings and love triangles. The male leads in both dramas have a simple, child-like, pure adoration for the female lead. However, while Love Alarm has some fantasy elements, Extraordinary You is definitely more fantastical. Extraordinary You is also lighter fare.

Both have super cute big height differences between the main couple. Both couples are students and have a friendship to romance relationship.

The two share the same genres ,while extraordinary you is a fantasy setting ,some scenes give similar vibes and are well developed romantic stories .