Angel Beside Me (2020)

Both have a poor FL who meets a supernatural ML when she is at her lowest point and falls for him later on.
Also both have a wholesome second lead couple, some reincarnation elements and bromance.

both dramas are about an angel coming down to earth and falling for a human girl even though it’s forbidden.

The mini series Secret Love (eps 9 + 10) has a story where an angel is sent down to help and understand a human, and ends up falling for her.

Similar themes of the afterlife and the supernatural and human realm intersecting.
Similar themes of love and relationships

Similar themes of humans and supernatural beings and love crossing the mortal human existence into other worlds

Supernatural beings and their interactions with mortals.
Similar themes of love and what other worldly beings do to it.

Similar themes of other worldly beings and their effects on human existence
Similar themes of love and sacrifice

Even though their plots are different, both ABM and SKL had kinda similar vibe in terms of cohabitation trope and a naive yet funny male lead who's completely dependent on the female lead as he is unfamiliar with the outside world. In ABM the ML is an angel with lost powers while in SKL, the ML is a rich heir with lost memories.

Similar themes of:
Forbidden love
Supernatural creatures
Humans in situations with supernatural beings

Both depict a similar interspecies love trope in which a supernatural character and a human are forced to cohabit. The Angel and Alien are innocent and curious about what's around them. Then, the human main teach them about simple thing on Earth and customs.