The "alsa xrun recovery apparently failed" bug seems to be solved here : https://github.com/pure-data/pure-data/issues/969
So, I downloaded the latest source code and installed Pd 0.51-4 on my Raspi (with Buster ->Linux version 5.4.72-v7+ (dom@buildbot) (gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)) #1356 SMP Thu Oct 22 13:56:54 BST 2020)
I use the onboard soundcard (bcm2835), as far as there is no input, I uncheck "input device". When I tested sound, there was no "alsa xrun recovery apparently failed" error message.
But some minutes later in "Pd noGui or GUI mode" + "Raspi console or graphic mode", the error is still there.