OK, good … but that device detection error is likely generated by a fastboot command (fastboot commands do get reported as ADB errors).
What is the terminal response to
fastboot devices
while the phone is booted to Fastboot mode?
eosinstaller installer does not work for all as seen from threads with that hashtag. Changing to the manual Install method (it uses a script, so not too hard) may be easier than debugging the installer.