If your class, study hall, etc. does not appear in your Classroom app, you can manually create the class and invite students to join.
Create your first class.
Open the Classroom app
on your Mac or iPad, then do one of the following:If this is your first time using Classroom, select Continue, enter the name you want your students to see (for example, “Mrs. Dawson”), select the image icon to take or choose a photo, then select Done.
If you’ve created your teacher name already, proceed to step 2.
Select Create Class, then enter the name for your class and an optional description. Select an icon and background color for that class, then select Create.
Invite students to join your class.
Your unmanaged nearby advertised class is ready for enrollment, and a student can browse for that class by choosing Settings > Classroom on their Mac. Students add the class by entering a four-digit invitation code that you provided. A student can join more than one class—by the same or different teachers—making it easy for students to move from room to room with their iPad.
If you’re not already in the class, select the class, select
, then select Invite 
.Note: It may take up to 10 seconds for the class to appear for nearby students.
Ask your students to add the class:
On a Mac with macOS 13 or later: Select System Settings > Classroom, and select Add Class name.
On a Mac with macOS 12 or earlier: Select System Preferences > Classroom, and select Add Class name.
When you’re ready for students to join, display the class invitation code on the Viewsonic board for all students to see.
After a student adds the class, that student appears in the window. A checkbox appears next to the students’ names, indicating they’re going to be part of this class.
Review the list of students and deselect the ones you don’t want in the class, then select Add.
You can add more students at any time.
from: https://support.apple.com/guide/classroom/create-unmanaged-nearby-classes-clac1c715b6a/web