I'd like to read some manga where the main girl already has some past sexual experience before meeting the MC. It doesn't have to be a romance, it can be any genre.

There's a tag for this: Female Lead with Sexual Experience

Using the Advanced Search feature in the right-hand sidebar you could search with this tag and filter on other genres you want to include or exclude. There's also a link to a dictionary of tags in there.

"We can not resort to simplistic or extreme solutions which substitute myths for common sense." ― Jimmy Carter