It runs inside Termux, which has a persistent notification to keep it open in the background. I believe I also extended the max phantom process to prevent it from being killed.
The Pixel device I have is from a family member and it is locked to Verizon, who won't unlock the bootloader. I'm sure there's a work around, but I didn't think it was worth the effort. PostmarketOS is rad though, I have it running on an ancient Windows Surface RT.
Just curious