It's Okay to Not Be Okay (2020)

there's no age gap in IOTNBO but in both dramas:
- the FL is rich (and has a great wardrobe) + has been sheltered (personalities differ though)
- FL pursues ML first and relentlessly chases after him
- has a ML who has things holding him back from starting a relationship with FL (in TFF its age gap and his responsibility as an adult, in IOTNBO its his responsibilities and her personality).
- both have great chemistry between leads
other than that plot varies wildly, but I think it's a good rec to keep in mind if you run out of directly similar ones.

Both have a mentally challenge child at home. Fully functioning, smart and genius in someway but mentally struggle in another way. Both have a very committed family member unconditional love

Both dramas are psychological rom-com and the main theme is mostly related to female leads. Both dramas have wonderful leads and a nice romance.

- Both dramas MASTERFULLY portray mental health issues
- Both dramas MLs have complex brotherly relationships which is beautifully portrayed and is so touching
- Brotherhood is a strong part of both dramas
- Both ML s work in healthcare settings
- Both MLs are very hot xD I mean it's Lee Dong Wook and Kim Soo Hyun <3
- Both are top-notch psychological mysteries

Similar:
- Self-care, personal growth, adapt and overcome
- Romance : Communication & great chemistry of our main couple, slow burn
- Not an usual drama : new twists and unexpected turns.
- Good OST
- Dysfunctional family

Not similar: In Run On, the atmosphere is light and fluffy, whereas in It's Okay To Not Be Okay, it's darker.

Feel are the same, healing love
And the guy are cold but warm
Female like the guy but also excell at her job