Traveling to Europe from banned countries on sweetheart exception

Europe is mostly locked out from the US due to COVID except for essential travel. Tourism obviously does not count, but some countries have made exceptions for visiting important family, fiance, or "sweetheart".

See this article and this policy page from Denmark.

Does anyone know where I can find out which countries will honor a transfer through their country? For example, I emailed Iceland and they said they would definitely allow me to travel Icelandair and transfer to Denmark through Reykjavík. I am specifically wondering about Portugal (TAP), as they have the cheapest flights. I emailed their immigration, and they sent me this long and very confusing response: pastebin because it is so long.

I would mainly like to hear from people who have traveled to Europe from banned countries already, and what their experience has been. There's almost nothing on the internet about this, so any information you can offer would be helpful.