The USB3.0 to ethernet adapter I ordered arrived yesterday, so installed freepbx on my c720 chromebook, which hasn’t been used years. Works great!
The tutorial: https://www.pbx.science/build-a-pbx/pbx-on-chromebook/
Thought about Raspberry Pi 4 before, but x86 CPU is prefered because such machine could be installed FreePBX distro directly.
In addtion, Pi is not cheap after adding case, SD card, power supply. You can find an used chromebook or chromebox on ebay, probably 40-50 bucks, then you will own x86 server with “free UPS” (if internal battery included and works)