In this post, I am sharing an option to create a Read Only table in SQL Server.
I also shared an article on how to create a read only database in SQL Server?

SQL Server: Script to make Database Read Only and Read Write

If you thinking to give a SELECT permission on the table, you have to give SELECT permission to particular group/user.
But, here I am talking about complete Read Only Table, which has by default only SELECT permission for all the users/groups.

How to create a Read Only Table?

Add one file group to database:

ALTER DATABASE my_database ADD FILEGROUP [Read_Only]

Create a new data file:

ALTER DATABASE my_database ADD FILE ( NAME = N'data_file_name', FILENAME = N'D:\data_file_path.ndf' , SIZE = 3072KB , FILEGROWTH = 1024KB ) TO FILEGROUP [Read_Only]

Create a table under newly created data group:

CREATE TABLE test_readonly (id INT) ON [Read_Only]

Load/Insert your data:

INSERT INTO test_readonly VALUES (1),(2),(3),(4)

Now, set READONLY to newly created file group:

ALTER DATABASE my_database MODIFY FILEGROUP [Read_Only] READONLY

Try to insert same records:
Now, you can’t insert/update/delete the data because a table is Read Only now.

INSERT INTO test_readonly VALUES (1),(2),(3),(4)

Msg 652, Level 16, State 1, Line 8
The index "" for table "dbo.test_readonly" (RowsetId 72057594042187776) resides on a read-only filegroup ("Read_Only"), which cannot be modified.