Textbox with “new line”

We tried several ways to make a textbox to accept the “enter”, newline, etc.. But we are still facing the same problems. Most of the “Third party” controls allow the user to format the text as he wants. Eg, add color, font, table, etc.. However, for most stylish websites, we do not want to allow the user to format the text that way.

Fluent Validation, different validation for each item in a list in Asp.NET Core

I´ve been trying to find a way to validate items inside a list, each with different validation rules. I came upon Fluent validation which is a great library but I can´t seem to find a way to do validation for each item individually. I got a faint idea from this similar thread (Validate 2 list using fluent validation), but I´m not sure how to focus it how I want.