C# alternative to Thread.Suspend() method

Thread.Suspend() method is obsolete as you know. I want to suspend thread immidiately when button click event comes. I used Thread.Suspend() and it works perfect but everyone suggest that using Thread.Suspend() method is not a good method to suspend the task. I used a flag to suspend the task but every time when a button click event comes, i have to wait to exit from task. I used Thread.IsAlive flag to wait the thread to exit but this method freezes form.

void ButtonClickEvent(object sender, ButtonClickEventArgs e)
 {
     TheadExitFlag = false;
 
     if(MyThread != null)
     {
         while(MyThread.IsAlive);
         //MyThread.Suspend();
     }
 }
 
 void MyTask(void)
 {
     while(TheadExitFlag)
     {
         // some process
         Thread.Sleep(5000);
     }
 }
 

How can i suspend the thread immidiately?

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