Normally I use
aptitude upgrade or
aptitude full-upgrade to get my system up to date. Since I am fiddling around with Vbox installation, I followed https://wiki.debian.org/VirtualBox strictly and added
deb http://httpredir.debian.org/debian/ sid main contrib non-free to
/etc/apt/sources.list and ran
apt update, which apparently gives much more information about the installation process than
aptitude including a lot of Error messages. So I started fixing these (e.g. NO_PUBKEY, superfluous cdrom entries, etc.). While searching the web to solve a few issues, I see the plasma update icon "Updates available" popping up. Okay, taking a look ... it shows "2584 packages to update" with more than 2 GiB to download ... and the count and volume are steadily growing as I write this question!
All seem to be not system relevant, just applications like Activity Pager, Akregator, and so on which I don't remember to have ever installed.
What did I do wrong? How to fix this? And why do I get updates for packages I don't recall to have ever installed?
I am running Debian Buster with KDE Plasma.
UPDATE: if the Sid line in sources.list is commented out, then the update request disappears; however something starts downloading from the internet (not sure yet what and why) whenever the network is connected