Solved my own problem - it turns out that the PicoScope 2204A can be detected, but only if it is connected to the Rpi after launching PicoLog 6. I don't recall seeing this spelled out in the manual.

Hi Andrew
(resurrecting old question...)
I am running Raspberry Pi OS (previously called Raspbian) Buster on a Pi 4 (8GB), but I also find that PicoLog (I downloaded the current 6-1-18) doesn't detect my newly purchased 2204A. I did not have this problem on Ubuntu 18.04
Thanks in anticipation
Simon

New to picoscope. 2204A just arrived today. I already had PicoScope 7 installed on my Ubuntu 18.04 from before (to try out the demo). But I read that 6 and 7 can coexist, and so went ahead, following the instructions at https://www.picotech.com/downloads/linux to install PicoScope 6. However, it tol...