The FuriPhone FLX1 meets all of your requirements:
- It runs the Debian-based FuriOS, which is FOSS.
- Among phones with Linux (excluding Android) preloaded, its specifications are among the best available, including a camera with PDAF and OIS, a 120Hz screen, and a replaceable 5,000 mAh battery. It also supports 5G and VoLTE, and has IP68 water resistance.
- FuriOS includes Android app support via a fork of Waydroid.
- The phone and the Linux distro are actively maintained.
- Furi Labs is based in Hong Kong.