@minkiu said in Is it possible to flash from TWRP (with .zip file)?:
While I managed to get adb working, once it boots into fastboot it just won't detect it
I had something similar on opensuse with the AppImage installer (would affect deb as well AFAIK). And the cause there was that I had adb and fastboot in /usr/local/bin. But when run with sudo (explicitly starting the installer with sudo or letting the installer use sudo internally), /usr/local/bin is not in the $PATH. And the command to detect if the phone is in fastboot mode ignores the custom paths you can specify so that doesn't help either.
So it might be worth a try to either place/softlink adb and fastboot in /usr/bin or adjust your system-wide sudo config to also include /usr/local/bin (or wherever you have installed adb/fastboot).