Contains books where the characters do not know at the beginning that they will be forming a reverse harem. The FMC has the develop each relationship at its own pace, which may result in some jealousy and angst between the MMC, until an agreement is found. Preferably they have some (believable) hold-ups before forming a relationship (enemies-to-lovers, common past, etc.)
Please only add the first book in a series

Both contemporary and paranormal RH welcome.
MM welcome.

No Omegaverse
I love a good Omegaverse but their premise (forming packs) doesn't fit with the idea of this list.
This includes other "worlds" were harems may be typical (shifters, fae, etc.)

No Instalust (or even worse instalove)
Let me give you an (exaggerated) example of what the FMC should not be thinking: "Oh no, I just met three super-sexy guys that I hate but can't help lusting over. What should I do? Never mind, they mentioned they might like sharing and that sound sooo intriguing"
This also means no fated mates or similar.