Houray! Today I found my address confirmation e-mail! Order date: October 19, 2017, confirmation e-mail October 25, 2021. Now looking at the accessories again I was thinking the OpenPGP card might be useful, so I ordered one to come with the phone.
@nerd7473: considering my old Huawei/ Google Nexus 6P it seems there are no official LineageOS nightly builds for it. There are unofficial builds on xda-developers.com… once I made the Librem5 my daily driver, I might try one of them. I had such builds before, on my first smartphone (an “HTC Desire S”).