Version 7 will introduce a new file type with MIME type
In the [en-US] UI it is named "ODF Master Document Template (*.otm)" in the save dialog.
I have tried to assign LibreOffice 7 as default application for .otm on Windows 10 doing this:
right-click > Open with > More apps
In the file explorer go to
"C:\Program Files\LibreOfficeDev 7\program\swriter.exe"
Using the checkbox "Always use this app to open .otm files"
the "Type" in Windows Explorer has still "OTM File" (would expect something like 'OpenDocument Master Document Template'),
the icon there is the Writer icon, where it should be a template-like icon.
the context menu has only Open, but should have 'New' and 'Open'.
Some problems might come from the situation, that Version 7 is still a developer build and it should be checked again with the release candidate.
I'm not familiar with that area of code. But to me it seems, that at least the icon is missing in sysui/desktop/icons/ and its reference in /core/desktop/util/officeloader.rc
there is a way to write the registry entries even for dev builds, iirc something like
probably this needs adding in
Tested with Version: 184.108.40.206 (x64)
Build ID: 04ba7e3f1e51af6c5d653e543a620e36719083fd
CPU threads: 8; OS: Windows 10.0 Build 18362; UI render: Skia/Vulkan; VCL: win
Locale: de-DE (en_US); UI: en-US
That version has system integration because it is a RC1. But still the icon is wrong. The *.otm document shows the icon of a simple Writer-document in Windows file explorer. It should be the same as for a .odm but in gray.
I see no icon for it in https://opengrok.libreoffice.org/xref/core/sysui/desktop/icons/hicolor
I have changed the summary accordingly.
I have now found that the system integration is unfortunately not correct. 'odm' has "New" and "Open" in context menu. It should be only "New". And 'otm' has only "Open", but it should be "New" and "Open". It might be, that there is something wrong with my Windows, so it would be good, if someone could check it with his installation of LO7RC.