Recommendations

Both shows story starts with accidental pregnancy because of One night stand between leads. Both shows have Rich/CEO ML and plain Jane setup for FL.

Both female went to the back to the past
Both where betrayed by their spouse
Both came for revenge on their husband

Peach blossoms vs pear blossoms;
Kunlun Mountain (it's even mentioned) vs Daze Mountain;
FL first weak, then strong;
FL hurt by ML;
ML is left to wait in the rain (FL doesn't want to see him and brings the rain over him);
FL forgives ML when she finds out how much he has done for her
ML sacrifices everything for FL and the world ;
ML returns after disappearing due to his sacrifice.
Wonderful OST.

Both dramas have Kim Hye Yoon in!
The male lead is in both drama famous in a way - football player and idol

Mature Main Leads.
FL gives second chance at love.
Green flag male lead.
Boss Employee Relationship.
Workplace Romance.
Green Flag Female lead.
Slow burn romance.
focusing and educating on a particular occupation/domain.

The main character's illness is brought by trauma and their other personality is trying to protect them

It's similar, because they are both about enduring feelings of one having a crush on a friend or classmate. Even though School Trip is based in a school setting, while Countdown also started at school (because that's where everything begun) and later to common places known to everyone. They are both about pursuing your crush, until you win them over, through glances, gestures and persistence.

Both shows feature an older woman and younger man romance. The FLs are positioned in a role of providing direction for the MLs and are very capable in their careers. The MLs only have eyes for the FLs from the start and pursue the FLs with sincerity-- the chemistry is very apparent. The MLs show a lot of character growth over time and want to prove that they can be a stable match. The SMLs are mature and not overly problematic. Both shows are in a corporate setting.

Both very healing, slow burns. imo FBF walked so TBT could run. There are still some cliche's and some bumpiness in the storyline for FBF. But these are both very refreshing, focusing on a slower life (ML lives a slower life) while FL works in a customer-first intense job (FL adjusts to living a slower life). The backgrounds of the characters are very different though, leads are dealing ways to navigate and heal from their trauma. imo, also, both relationships really don't make sense at first, both sides do not want to burden the other side, but they show their love in unique ways. The production/storyline quality is a bit better for TBT, but I think the ML was a little too perfect, whereas FBF really showed ML and FL's strengths and weaknesses.

Both try to solve cases through time travel

Both: thriller, crime, fantasy, mystery

The difference:
In Erased ML becomes a child again and sees this opportunity as a second change to prevent this from happening.

In Tunnel ML stays the same and teams up with a new investigation partner.

Both have Genres: Thriller, Mystery
Both: investigation, crime, suspense
Both: disappearing case after moving
Both: the sibling trying to solve the case

Both have a murder case involving their parents
Both series are about trying to solve their mothers murder cas.
Both are a thriller, crime and mystery genre

Differences:
Erased is adapted from a manga
Erased involves time travelling, Ugly takes you back by looking back in the past by memories.
Erased is a micro JDrama
The Ugly is a Korean movie.

If the novel storyline is followed faithfully, then this will be a reverse harem situation similar to Lost You Forever. Obviously the genres are different, but both are female-centric stories focused on the female lead overcoming adversity and navigating at least 3 men in their lives.

- Both Thriller, Crime.

- Both sons trying to solve a murder case where their fathers are involved in.

- Both series have good actors and story telling.

- In both cases the sons try their best to get to know the truth and getting the larger picture who are all involved.

- In both you get to know the story about the victim.

Differences: Confession is a drama, The Ugly is a movie and has more a steadfast storytelling.

Confession has Lee Jun Ho
The Ugly has Park Jeong-min

- unraveling a murder
- in The Ugly a journalist tries to uncover a murder story, in The Confession it’s a lawyer
- same pace of how the story unfolds
- same kind of genre mystery, thriller and crime.
- in both movies you go back in time and present and see it from different perspectives.