Hi all, just wanted to thank everybody involved with GrapheneOS. 
Found it recommended in a blog (Mike Kuketz), followed up reading here and on the website, decided it is what I have been looking for, bought a 4XL second-hand and installed GOS two days ago, following the official installation guide without any problems (from a live Lubuntu 20.04).
The step-by-step-guide really covers the whole process. 
Looking forward to customizing (e.g. profiles / users), migrating data (from old phone) and using (with a huge boost in security and privacy 😀).
So again: Thanks a lot to all those who contribute to this project!!! 👍️