Happy to report that I can now connect an android phone to a Garmin bike computer using an OTG cable. No root required! This basically resolves the question posed by the OP and allows the user to create and transfer routes to a bike computer from a phone or tablet without wifi or data connection. First, download the USB OTG checker app to verify your android device allows OTG connection. You'll also need the EZ File Explorer app. You then need to enable USB debugging for your device. Next, open the EZ File Explorer app, connect to your device with the OTG cable and wait for the USB drive to display. If 0% drive usage is indicated, then another app is interfering. Go into Apps/Settings and choose "no" for the "draw over other apps" function on similar file sharing/management apps you have installed. No guarantees here, but easy enough to try.