Until we are using tdm's driver, there will be undesirable interactions between the F(x)tec's custom keymap and the keyboard language selection in Android. Have you selected a language and layout as directed by the persistent notification to "Configure physical keyboard"?
Don't do that. 😜
I can attest that a Pi4 works flawlessly so far for flashing for me. Just had to do:
sudo apt-get install -y android-tools-adb android-tools-fastboot
to install the tools needed.