You should start by checking the SaveAs method.
You should have noticed that when you typed the '.' after ActiveDocument that SaveAs was not present in the list of intellisense options. Instead you get offered SaveAs2.
The reason for this is that SaveAs is deprecated and has been superseded by SaveAs2. The old method is still available but its continued presence in future releases of Office/VBA cannot be guaranteed.
SaveAs2 on its own just adds a new option (compatibility mode) to the SaveAs method. Neither SaveAs2 or the ability to choose compatibility will resolve your problem. Instead you have to use F1.
In the VBA IDE placing the cursor on any keyword and pressing F1 will bring up the MS help page for that keyword (if the keyword exists). If you press F1 on SaveAs you won't get any help, jest a generic page, but if you press it whilst on SaveAs2 you will get this help page.
https://docs.microsoft.com/en-us/office/vba/api/word.saveas2?f1url=https%3A%2F%2Fmsdn.microsoft.com%2Fquery%2Fdev11.query%3FappId%3DDev11IDEF1%26l%3Den-US%26k%3Dk(vbawd10.chm158007864)%3Bk(TargetFrameworkMoniker-Office.Version%3Dv16)%26rd%3Dtrue
When you look at the help page you will see that the second parameter for the SaveAs2 method is 'FileFormat' which is
The format in which the document is saved. Can be any WdSaveFormat constant. To save a document in another format, specify the appropriate value for the SaveFormat property of the FileConverter object.
The fact that SaveAs (Now SaveAs2) didn't complain when you only provided a filename means that a default option has been supplied by the method, which is most likely to be the ' save this document as a word format document' option (wdFormatDocumentDefault).
For you to save your document as a macro enabled word template you would need to specify the enumeration constant , wdFormatXMLTemplateMacroEnabled.
e.g.
wdApp.ActiveDocument.SaveAs "H:\Word\B.docm", wdFormatXMLTemplateMacroEnabled
You would also have got to this option if you had recorded a macro during which you saved a document as a template to see what Word would do in the same situation (admittedly not always helpful).
Sub Macro1()
'
' Macro1 Macro
'
'
ChangeFileOpenDirectory _
"C:\Users\user1\Documents\Custom Office Templates\"
ActiveDocument.SaveAs2 FileName:= _
"C:\Users\user1\Documents\Custom Office Templates\test.dotm", FileFormat _
:=wdFormatXMLTemplateMacroEnabled, LockComments:=False, Password:="", _
AddToRecentFiles:=True, WritePassword:="", ReadOnlyRecommended:=False, _
EmbedTrueTypeFonts:=False, SaveNativePictureFormat:=False, SaveFormsData _
:=False, SaveAsAOCELetter:=False, CompatibilityMode:=15
End Sub
Good luck with your further endeavours.