Searching the net for printing envelopes they all say click Insert then Envelopes. However my Insert does not have an Envelopes option. What is going on here?
In LibreOffice 6.0.5.1 on Windows, the last item of Insert menu of Writer is Envelope.... So, if your version doesn’t have it, then at least specify the version, instead of thet anonimous “my Insert” which (combined with the common tag) doesn’t allow to guess which version and which application is used, let alone OS (which may affect this, if a distro has this function in an optionally installed package).