Packaging Klayout

Project information: KLayout is a mask layout viewer and editor for the chip design engineer. It is a Qt-based application.

Name: KLayout
Homepage: www (dot) klayout (dot) de (I can’t include the link because of discourse rules about linking)
License: GPL-3.0+
Upstream has been contacted: See here

I have already prepared a manifest for submission to Flathub here. In the link above about upstream contact, the developer was asked about creating a flatpak two years ago and said he would look into it (a working manifest file was given along with the original request). I asked again two weeks ago and provided a link to my updated manifest. So far there has been no response from the developer though he has pushed some new commits to the repo since my post. I think a fair summary of the situation is that the developer does not care about packaging KLayout as a flatpak. Since it is GPL-3.0+, is there any reason to try to get explicit permission from him or can I submit my manifest to Flathub?