I removed x16emu and installed it again and then I got these messages in Raspberry Pi OS Buster (most full-upgraded) on Raspberry Pi 4B:
$ sudo snap install x16emu
2021-03-30T13:06:26+02:00 INFO snap "x16emu" has bad plugs or slots:
audio-playback (unknown interface "audio-playback")
x16emu r38 from Alan Pope (popey) installed
I removed x16emu and installed it again and then I got these messages in Raspberry Pi OS Buster (most full-upgraded) on Raspberry Pi 4B:
Sound works in x16emu.