I have just finished watching Someday or One Day (2019) - Taiwanese Drama and I highly recommend it.
It is romance but not considered light-hearted generally and is not really historical.
Time travel between 1998 ~ 2019. Script was really well-written and skillfully planned, probably the one of the best time travel plot out of all those I have watched. I HIGHLY SUGGEST YOU GO IN FULL BLIND without even reading the synopsis/spoilers/reviews at all if you are interested.
I only watched kdramas mainly and those that contains time-travel elements are:
365: Repeat the Year (2020)
Chicago Typewriter (2017)
Live Up to Your Name (2017)
Life on Mars (2018)
Moon Lovers: Scarlet Heart Ryeo (2016)
Mr. Queen (2020)
Queen In Hyun's Man (2012)
Sisyphus: The Myth (2021)
Splash Splash LOVE (2015)
The King: Eternal Monarch (2020)
You may check it out if you are free and see which ones they interest you, some might not have romance and might not be historical also.
AH :
