expression not in aggregate or GROUP BY columns

I have a table that contains the following columns:
ProductID, ProductName, Price, CategoryID.

The goal is to print all the details (ProductID, ProductName, Price, and Category) about the most expensive product.

I executed the following query:

str = "SELECT ProductID, ProductName, MAX(Price) AS MaxPrice, CategoryID FROM Products;";   

However, the exception mentioned in the title appears, and I do not find a reason for the exception appearance. I searched for explanations on the following links:

• Expression not in aggregate or GROUP BY columns Exception

• Aggregate columns not in group by

I have also read and practiced in SQL Lesson 10: Queries with aggregates (Pt. 1)
According to my checking in SQLBolt, the way I wrote the query is acceptable.

After reading and practicing, I still do not understand why I need to use the GROUP BY here. It’s not that I need to present the maximum price of each group…

Thank you very much beforehand!