They are both based on the same novel, each country gave their version a different tone.
I think it's always interesting for the viewers to watch both and decide the pros and cons of both.

Both dramas have a group of friends trying to right wrongs and solve mysteries.
Both dramas reverse the usual gender roles with male leads that use their brains instead of their fists and female leads who are good at fighting.

In both historical dramas Chen Xiao plays a similar character: a smart and strong man falling for a strong woman, while their pasts put their future in danger.

Both are BLs with a slightly supernatural element of sensory loss that's connected to their "other half".

There is something very similar in the aesthetics of the two BL dramas. They both use harsh light and deep shadows to symbolise a problematic states of mind. Both dramas have a main character with an unresolved past that gets in the way of a new love.

Although one of them is a BL, they both deal with a main character that has seemingly gone to the dark side and both have time jumps.

Both dramas are BLs that deal with men who are thrown into a different reality.
Both dramas focus on the comedy and romantic aspects instead of the science behind it.

Although both dramas have a completely different story and vibe, they both deal with what can happen when people don't conform to their gender.

Both dramas have a ruling father who makes his three sons compete against each other over the throne, but then doesn't understand why they are trying to kill each other. In both dramas one of the sons pretends to be dumb and weak to blindside everyone.

Same author, similar themes.
Same kind of team work in law enforcement.
Both have a gritty urban atmosphere.
Both have a friendship/romance/bromance that tries to survive in a world full of inner and outer conflicts.

They both have similar themes of a women trying to progress in a competitive and male dominated industry, both have a mentor ML (although in very different ways) and a slight romance that isn't the main focus.

Both dramas focus on the lives and loves of different airport personnel. NF teaches more about the different jobs in an airport, while FTY deals more with the inner politics behind the scenes, but both are full of beautiful people and majestic aircrafts.