Both are medical drama
Both has revenge as underlying theme
Both have illegal heart transplant in it
Vibe of the story is same

- In TFS set in 1997, the detective team is working on catching a drug ring while in DNAD set in 1950, the police team is trying to take down a group of agents/rebels who are plotting to destroy the city (more on political side).
- There is bromance between two male leads in both dramas (though they doesnt trust each other at first but then becomes greatest support for eachother) and camaraderie between team members with slight comedy here and there.
- There is also brotherhood and betrayal in both dramas where ML is left in a dilemma.
- Both drama give the same vibe overall.

Both the dramas have same kind of suspense reveal.
In both dramas, incident happens around a group of high school friends in the past which gets solved in the present.

You suspect everyone till the end. All of them are suspicious and hiding something. You can only trust the two main leads ie. In connection there is ML and FL while in black out it is two MLs. ML in connection is Jisung afterall so i dont think I have to explain the level of acting.

Both are revenge dramas with uncovering conspiracies.
One of the leads hide their identity in both dramas because of their past incidents - MLC it is ML and in TD it is FL
In case of MLC it is two male leads and bromance/friendships, in TD it FL and ML and romance also friendships as well.

In stranger we have an upright prosecutor ML who is emotionless due to a condition and a police officer FL who is strong and independent. While in connection there is an upright police officer ML who is struggling with drug issues and a reporter FL who is bold. There is no cringey romance in both but the level of understanding between the leads is amazing. The vibe of both dramas are similar and you keep asking who might be the culprit throughout the story.

Group of people trying to uncover mysterious death of a person close to them (especially to main leads). There is a hacker in the group and illegal obtaining of evidences also. Team dynamics is great plus there is comedy also in between balancing the humor sense of drama.

Both are wuxia drama.
Both dramas have 3 MLs who trust each other and has amazing teamwork that helps them to solve cases together.
Bromance at its best in both drama.
conspiracy theories that finally ends with a war.

Both are wuxia dramas with investigation/small case solving which will eventually lead to a bigger case/main plot of the drama.
UTP has slow burn romance with amazing chemistry between the leads (both ML and FL are strong and independent) while MLC has a slow burn bromance/friendships (lol) and ofcourse chemistry between three leads of MLC is fantastic (bickering trio)

Both drama has similar vibe, humor,action,detective skills and wonderful chemistry between leads.