Comments here have said the story is similar to Tiararose x Aquahorse, which is about right.
As a Japanese WN reader said, "Barring the small minority of genuinely interesting stories (you find on webnovel sites), most of the stuff you find here are ripoffs (of other webnovels)."
https://www.google.com/amp/s/frogkun.com/2019/07/01/i-tried-thinking-about-the-common-isekai-slave-circumstances-realistically/amp/
@heyykelleyn iirc Prince Waterhorse came out in 2016, while the source WN for this one came out in March 2020. That said, Villainess Doted By Crown Prince is still pretty popular with its Japanese followers. Author's written 10 webnovel arcs (currently planning an 11th), and they all got published as LNs.
https://www.kadokawa.co.jp/product/322001000655/