Cannot insert explicit value for identity column when SaveChanges

Question

I have a model named AcademicLevel:

public class EducationLevel
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    public virtual ClassName ClassName { get; set; }
    public virtual SectionName SectionName { get; set; }
    public int Years { get; set; }
    public virtual Gender Genders { get; set; }
    public virtual MediumName Medium { get; set; }
    public int MaxCapacity { get; set; }
    public virtual WorkStation Campus { get; set; }
    public virtual AcademicSession AcSession { get; set; }
    public virtual ICollection<Student>? Students { get; set; }
}

The model class for WorkStation is

public class WorkStation
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int? Id { get; set; }
    
    public string Name { get; set; }
    
    [Required]
    public virtual Company? Company { get; set; }
    
    [Required]
    public string Address { get; set; } = string. Empty;
    
    public virtual ICollection<EducationLevel>? Classes { get; set; }
    public virtual ICollection<ApplicationUser>? AppUsers { get; set; }
}

I am using a Windows UserControl to get the values of all the properties on the click event of a button.

EducationLevel cls = new EducationLevel()
        {
            MaxCapacity = Convert.ToInt32(MaxCapacitySpinEdit.EditValue),
            Years = Convert.ToInt32(YearsSpinEdit.EditValue)
        };

cls.ClassName = (ClassName)classNameBindingSource.Current;
cls.SectionName = (SectionName)sectionNameBindingSource.Current;
cls.Genders = (Gender)genderBindingSource.Current;
cls.Medium = (MediumName)mediumNameBindingSource.Current;
cls.Campus = Behaviour.LoginInfo.User.Office;
cls.AcSession = _context.AcSessions.Where(s => s.Id == 1).FirstOrDefault();

_context.Classes.Add(cls);
_context.SaveChanges();

The CREATE TABLE for AcademicLevel or cls is below:

USE [AIMS_db1]
GO

/****** Object: Table [dbo].[Classes] Script Date: 10/23/2023 12:02:07 AM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[Classes] 
(
    [Id]                 INT            IDENTITY (1, 1) NOT NULL,
    [ClassNameId]        INT            NOT NULL,
    [SectionNameId]      INT            NOT NULL,
    [Years]              INT            NOT NULL,
    [GendersId]          INT            NOT NULL,
    [MediumId]           INT            NOT NULL,
    [MaxCapacity]        INT            NOT NULL,
    [CampusId]           INT            NOT NULL,
    [AcSessionId]        INT            NOT NULL,
    [EntryTime]          DATETIME2 (7)  NULL,
    [CreatedByUser]      NVARCHAR (MAX) NULL,
    [LasteModifiedTime]  DATETIME2 (7)  NULL,
    [LastModifiedByUser] NVARCHAR (MAX) NULL,
    [Version]            INT            NOT NULL
);
GO

CREATE NONCLUSTERED INDEX [IX_Classes_AcSessionId]
ON [dbo].[Classes]([AcSessionId] ASC);
GO

CREATE NONCLUSTERED INDEX [IX_Classes_CampusId]
ON [dbo].[Classes]([CampusId] ASC);
GO

CREATE NONCLUSTERED INDEX [IX_Classes_ClassNameId]
ON [dbo].[Classes]([ClassNameId] ASC);
GO

CREATE NONCLUSTERED INDEX [IX_Classes_GendersId]
ON [dbo].[Classes]([GendersId] ASC);
GO

CREATE NONCLUSTERED INDEX [IX_Classes_MediumId]
ON [dbo].[Classes]([MediumId] ASC);
GO

CREATE NONCLUSTERED INDEX [IX_Classes_SectionNameId]
ON [dbo].[Classes]([SectionNameId] ASC);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [PK_Classes] PRIMARY KEY CLUSTERED ([Id] ASC);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [FK_Classes_AcSessions_AcSessionId] 
        FOREIGN KEY ([AcSessionId]) REFERENCES [dbo].[AcSessions] ([Id]);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [FK_Classes_ClassNames_ClassNameId] 
        FOREIGN KEY ([ClassNameId]) REFERENCES [dbo].[ClassNames] ([Id]);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [FK_Classes_Genders_GendersId] 
        FOREIGN KEY ([GendersId]) REFERENCES [dbo].[Genders] ([Id]);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [FK_Classes_Mediums_MediumId] 
        FOREIGN KEY ([MediumId]) REFERENCES [dbo].[Mediums] ([Id]);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [FK_Classes_SectionNames_SectionNameId] 
        FOREIGN KEY ([SectionNameId]) REFERENCES [dbo].[SectionNames] ([Id]);
GO

ALTER TABLE [dbo].[Classes]
    ADD CONSTRAINT [FK_Classes_WorkStations_CampusId] 
        FOREIGN KEY ([CampusId]) REFERENCES [dbo].[WorkStations] ([Id]);

I get an error

Cannot insert explicit value for identity column in table WorkStations when IDENTITY_INSERT is set to OFF

While I am not trying to save WorkStations but EducationLevel only, why do I get this unrelated error?