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The best answer I can think of for you would be Tokyo Necro https://vndb.org/v13666. Dual protagonists (one female, one male, all love interests for both are female) and another Nitro Plus game like Saya. A rom-com / slice of life that might be worth trying out if you're REALLY looking to stretch your boundaries would be Sugar * Style https://vndb.org/v24320 it takes place in college, with the youngest love interest being an 18 year old freshman if I remember right...sorry if I don't. And the obvious answer if you enjoyed Huniepop would be Huniepop 2.

Mashiro Iro is now available for purchase alongside Sana Edition on Steam with 40% launch discount (The xeet for the proof below). Feel free to get it from Steam or Johren (Because it's not available in the other stores yet), and have fun.