Huh. I was quite sure I had switched back, but apparently I forgot. To those running into this topic later, I followed this guide, except that I apparently hadn’t run sudo rm /etc/apt/sources.list.d/a2dp.list as described there.
Thanks for the very prompt help Sam! I ran the command again and then did a manual install, and again received an error message, this time about armv7-udisks-osmc: logs. But otherwise it does not say there are any updates any more, so I guess it’s all good now?