On cloud based Project 3 or project 5 or project professional 21 can you assign a task to a resource for say 10 days but set it so that they will only work 30% of their time on it?
John_Wilson0801, When you say project 3 or project 5 are you referring to the desktop version of Project available with either of those plans or are you referring to Project for the Web?
For Project Pro 2021 or other desktop versions, set the task type to Fixed Duration. Enter a duration of 10 days and then assign the resource at 30%.