Haven't figured it out yet, but I think it has something to do with the readline() library used in bluetoothctl, and changing colors around the prompt. I'm running over ssh on a Gnome Terminal 3.28.2. A simple workaround is to start a new terminal in the background >xterm & and then run bluetoothctl...

Running bluetoothctl on Ubuntu 20.04 and Pi4b has garbled lines. At the beginning of each line are unprintable characters that are not readable and obscure the first few characters of each line. After these characters, the rest of the line is readable. The app does appear to be working as expected; ...

Wow, PhilE, what an excellent answer. Thank you.

I have read most (not yet all) of the posts, and it appears what to in order to have the mini Uart used for BT and the PL011 Uart available for using on hats is (for Jessie, Nov., 2017) to add the following to /boot/config.txt enable_uart=1 dtoverlay=pi3-miniuart-bt core_freq=250 What baud rate woul...