It doesn’t have to have a romance with a younger man necessarily. Just stories with older females. I’m kind of interest in those at the moment.

Hmmm... Just a few ones come to mind.
Here:
Raise wo Chikatte Tensei shitara Taihen na koto ni natta: The MC is a 39 years old woman. She was in love with a knight in her past life as princess, but they couldn't stay together because of social standing. After reincarnating, she met with the man she was in love with, but their age gap is pretty big now. He remembers his past life tho, and wants to have a relationship with her. Older woman x younger man romance. Modern setting.
A Wicked Tale of Cinderella's Stepmom: Webtoon. Basically she reincarnated into the body of Cinderella's stepmother. Her husband died, so she has to take care of her three daughters (stepsisters and Cinderella). And prevent the story from going exactly the same way. She is 37 years old. The possible ML is a little bit younger than her, if I remember well. Also, Mildred is a strong female lead, in my opinion.
Those two are the ones that fit best, I think.
------OTHERS-------
The Remarried Empress: Webtoon. Fantasy. It's a slow-paced story and pretty good. Navier is a strong woman and I really love her. She is 23-25 years old, so she's not exactly in her 30s, but... She's pretty mature, if that helps.
Yuese Mitang: Manhua. 33 years old woman x 20 years old man. I don't know how good this story is, because there are only 8 chapters in english.
Hiru to Yoru no Oishii Jikan She is around her 30s/40s. I'm unsure if there is any romance here, but if there is it's older woman x younger man too. However, I don't think it's josei. And it's been a while since I read it, but I think it's told mostly by the guy's perspective.
I haven't read Nana and Toukyou Tarareba Musume yet, but I was recommended because they focus on women around their 30s so yeah. Maybe you can check it out.
I don't know many like that, but I hope it still helped. Maybe you'll also like Love War's Victory?
Well, I think that's all. Sorry if you were looking for modern setting only. I focused more on age than plot here.

Ane no Kekkon
Otoko no Isshou
Udon no Hito
Watashi no Shounen (TAKANO Hitomi) (The MC is in her 30s towards the end)