Both have older FL/younger ML romance
Both strong FL who is determined to live fuller lives
Both have ML who support the FL

Caution: In the coolest world, ML does not appear until the middle of the drama.

Both have leads going into a manga/novel about unexpectedly.

Both have female leads wanting to change their destiny as a scheming second leads into female leads.

They have the same vibe. Both have music that evokes nostalgia. Both have sibling-like childhood friends that transitioned into a relationship. Both FLs have hairstyles of short bob with bangs in high school. Reply 1998 focused more in the HS life of the main characters while Go Ahead focused more on their mid-20s