The new OS uses a different sound setup based on pulseaudio, whereas Sonic Pi is designed to use Jack. Have a look here for a temporary fix which can be applied to my 3.2,2 version.
I am currently testing a new .deb file for a beta version of sp3.3.0 which will hopefully be released within the next few weeks which works with the new sound setup. Once installed (reboot to pick up the module installed) you should be able to select the sound output by right clicking the loud speaker icon.
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