Hello @hehip,
for helping we would need to know more information. How long have you been waiting for installer before you decided to turn it off? In some steps there is need to watch your phone and confirm actions the installer made in fastboot. For example you need to confirm "Reboot to recovery" manually on your phone. I think installer claims it is "flashing firmware" but in reality it is waiting for recovery to boot up.
Today I successfully flashed FP3 from Linux using installer 0.10.0, maybe you can try Appimage if snap version is older one. You can read my latest experience here:
https://forums.ubports.com/post/79146