After the file type field is created, the UI does not allow the size of the file type field to be updated., however, this can be done using the SDK.
UpdateAttributeRequest

Create a console application and run the below code to update the size of the file type field.

App.config

<connectionStrings>
    <add name="DataVerseConnection" connectionString="AuthType=ClientSecret;Url=https://org.crm8.dynamics.com;ClientId=6fd6aec2-0000-0000-0000-c99021cdc4ed;ClientSecret=0000~s1pTTBTbY1YZp9Td0000C0RUifBB9Bxxxx;"/>
  </connectionStrings>

public class UpdateFileAttributeMetaData
    {
        public static IOrganizationService _sourceservice;
        public static OrganizationServiceContext _sourcecontext;

       public static void Main(string[] args)
        {
            var sourceconnectionstring = ConfigurationManager.ConnectionStrings["DataVerseConnection"].ConnectionString;
            _sourceservice = GetServiceProxy(sourceconnectionstring);
            _sourcecontext = new OrganizationServiceContext(_sourceservice);

            FileAttributeMetadata fileColumn = new FileAttributeMetadata();
            fileColumn.SchemaName = "new_filetypefield";
            fileColumn.LogicalName = "new_filetypefield";
            fileColumn.DisplayName = new Label("Sample File Column", 1033);
            fileColumn.RequiredLevel = new AttributeRequiredLevelManagedProperty(
                AttributeRequiredLevel.ApplicationRequired);
            fileColumn.Description = new Label("Sample File Column updated", 1033);
            fileColumn.MaxSizeInKB = 80 * 1024; // 80 MB
            UpdateAttributeRequest updatefileColumnRequest = new UpdateAttributeRequest();
            updatefileColumnRequest.EntityName = "account";
            updatefileColumnRequest.Attribute = fileColumn;
            _sourcecontext.Execute(updatefileColumnRequest);
            Console.WriteLine("update success");
        }

        public static IOrganizationService GetServiceProxy(string connectionstring)
        {
            CrmServiceClient conn = new CrmServiceClient(connectionstring);
            if (conn.OrganizationServiceProxy != null)
                return conn.OrganizationServiceProxy;
            else
                return conn.OrganizationWebProxyClient;
        }
    }

File size before the update

File size after the update

Articles related to file type field :

beyondd365.dev/move-attachments-from-file-t..