Are opinions considered sentences in Logic?

I am beginning to read the book titled forallx An Introduction to Formal Logic by P.D. Magnus. This is an open source book. On page 4 Magnus states:

In this open source book found here: https://math.libretexts.org/Courses/Fullerton_College/Math_100%3A_Liberal_Arts_Math_(Claassen_and_Ikeda)/05%3A_Logic/5.01%3A_Logic_Statements the author states that opinions don’t count as sentences because one person might consider it true while another might consider it false.This author wouldn’t consider “Rhubarb is tasty.” as a sentence. So which definition is correct to use? Thank you!