I have an AfterUpdate user trigger.  The test class is below but I keep getting the following error at the UPDATE line...
System.DmlException: Update failed. First exception on row 0 with id 00560000001A1zeAAC; first error: INSUFFICIENT_ACCESS_OR_READONLY, Cannot insert a user with this profile: []

I have tried without runAS and with runAs and both give the same error!  I need to create an active user then I need to deactive that user which would fire my trigger that is the business requirement.

Any ideas?  I thought I found and Idea that asks to allow updating user records in a test (ones that are created by the test itself).  Is there a way to resolve this issue? Thanks in advance.

@isTest
public class SM_User_Trigger_Test {
    @testSetup static void createUsers() {
        Profile pf= [Select Id from profile where Name='Standard User'];
        List<User> UserList = new List<User>();
        User user = new User();
        
        String orgId=UserInfo.getOrganizationId(); 
        String dateString=String.valueof(Datetime.now()).replace(' ','').replace(':','').replace('-','') ;
        Integer RandomId=Integer.valueOf(Math.rint(Math.random()*1000000)); 
        String uniqueName=orgId+dateString+RandomId; 
        User u = new User(firstname = 'Test1', 
                         lastName = 'Tester', 
                         email = 'test1.tester' + '@somecompany' + orgId + '.org', 
                         Username = 'test1.tester' + '@somecompany' + orgId + '.org', 
                         isActive = true,
                         EmailEncodingKey = 'ISO-8859-1', 
                         Alias = uniqueName.substring(18, 23), 
                         TimeZoneSidKey = 'America/Los_Angeles', 
                         LocaleSidKey = 'en_US', 
                         LanguageLocaleKey = 'en_US', 
                         ProfileId = pf.Id
                        ); 
        UserList.add(u);
        insert UserList;        
    }    

    static testMethod void testCase1() {
        Profile p = [SELECT Id FROM Profile WHERE Name='System Administrator'];
         User u1 = new User(Alias = 'newUser', Email='newuser@testorg.com',
         EmailEncodingKey='UTF-8', LastName='Testing', LanguageLocaleKey='en_US',
         LocaleSidKey='en_US', ProfileId = p.Id,
         TimeZoneSidKey='America/Los_Angeles', UserName='newuser@testorg.com');

          System.runAs(u1) {
            User User =  [SELECT id, isActive FROM User LIMIT 1];
            System.debug('User: ' + user);
            User.isActive = false;        
            test.startTest();
            Update User;
            test.stopTest();
        }
    }
}