How To Keep Running Program When Other Command Button Clicked

Hello Brother,

I need your golden hands to solved the code as below,

Option Explicit
Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)
Sub FillBottleA()
Application.ScreenUpdating = False
    Const valIncrement As Double = 2
    Dim intMax As Integer
    Dim intIndex As Integer
    Dim intCalc As Double
    
    intMax = 50
    
    For intIndex = 1 To intMax
        DoEvents
        intCalc = intCalc + valIncrement
        UserForm1.TextBox1 = Round(intCalc, 1)
        Sleep 100
    Next
Application.ScreenUpdating = True
End Sub

Sub FillBottleB()
Application.ScreenUpdating = False
    Const valIncrement As Double = 2
    Dim intMax As Integer
    Dim intIndex As Integer
    Dim intCalc As Double
    
    intMax = 50
    
    For intIndex = 1 To intMax
        DoEvents
        intCalc = intCalc + valIncrement
        UserForm1.TextBox2 = Round(intCalc, 1)
        Sleep 100
    Next
Application.ScreenUpdating = True
End Sub

This code will use to run in UserForm1 under CommandButton1 and CommandButton2, please see the file attachment for detail.
My question is,
1. When the program is running under CommandButton1, then I clicked CommandButton2, the running program will be stopped, not continues running.
What code should i write to protect the running program if other CommandButton will be clicked?
2. If the program running in UserForm1, then i moved to UserForm2, also the program stopped running.
What code should i write it to protect the program to continues running though i opened other UserForm?

Thanks in advance for any small helps and efforts.

Best Regards,
Iqbal