Create scheduled task programmatically without using management portal "Task Scheduler Wizard"

Yes, it's possible. For this you need to create class of the task. I used it to create server-monitoring sheduled task, that send me eamil. For example, i have class, that contains parameters of futured monitoring tasks (like task-name, period, timestart, timefinish, activity, description and so on), and contain method to create task:

Another example which I use in Covid-19 online dashboard to update the data:

ClassMethod CreateTask() As %Status
{
    Set task=##class(%SYS.Task).%New()
    Set task.Name = "Update data"
    Set task.NameSpace=$Namespace
    Set task.TimePeriod=0 // Daily
    Set task.TimePeriodEvery=1 // Every 1 day
    Set task.DailyFrequency=1 // Run Several times in a day
    Set task.DailyFrequencyTime=0 // Run every x minutes
    Set task.DailyIncrement=60 // # of minutes between runs
    Set task.DailyStartTime = 0 // Start at 00:00:00
    Set task.DailyEndTime = 86399 // End at 23:59:59
    Set task.StartDate = $p($H,",",1) // Start today
    
    Set taskdef = ##class(Covid19.UpdateTask).%New()
    Do task.AssignSettings(taskdef)
    Set task.TaskClass=$classname(taskdef)
    
    Set st = task.%Save()
    Return:$$$ISERR(st) st
    Return ##class(%SYS.Task).RunNow(task.%Id())
}

But you need to have the class,  Covid19.UpdateTask in this case:

Class Covid19.UpdateTask Extends %SYS.Task.Definition
{

Method OnTask() As %Status
{
    return ##class(Covid19.Utils).DailyUpdate()
}

}

HTH

BTW, this project could help you schedule a task programmatically via cron expression.