Is their any way (Macro) to save files in older version as default in coreldraw 2021

I think you need to use a macro to do it automatically.
You can simply record a macro but you may need to tweak the resulting code to get it right.

Here's the code for a macro I use in Draw 2020, that saves back to version 2018.
The line ".Version = cdrVersion20" is where you set desired version, and "20" actually 2018.
Possible that it may look slightly different depending on what version you are saving back to.

Sub Save_as_version_2018()

Dim Path As String
Dim Name As String
Path = ActiveDocument.FilePath
Name = ActiveDocument.FileName

Dim OrigSelection As ShapeRange
Set OrigSelection = ActiveSelectionRange
Dim SaveOptions As StructSaveAsOptions
Set SaveOptions = CreateStructSaveAsOptions
With SaveOptions
.EmbedVBAProject = True
.Filter = cdrCDR
.IncludeCMXData = False
.Range = cdrAllPages
.EmbedICCProfile = False
.Version = cdrVersion20
.KeepAppearance = True
End With
ActiveDocument.SaveAs Path + Name, SaveOptions
End Sub

Alternative operate with files In CorelDRAW
Open / Import / Save in version
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