I think that for that type of use case, you might want to give Droidian a shot now. To be honest, I was and am very tempted to use it as my daily driver (especially now I’ve learned that nextcloud-desktop actually works), but GrapheneOS on the later Pixel model is just nicer and quicker. But as a second device with a specific purpose like you say, I think that might actually work well today.
I’m surprised I enjoy the frustration so much. I think messing around with phones and other devices like this is my Sudoku.