Why are unsupported updates installed by default ?
I just saw this question on reddit, and I wonder if others too would benefit from the answer (okay it’s maybe me saving time so I can just point people here 
instead of answering)
I just installed Lubuntu 20.04 LTS and I’m totally new to linux.
When I opened software sources and clicked updates I saw that “Unsupported updates” had a tick by default, and I removed that but I wonder if I shall leave that on…
The “Unsupported updates” option is a way of referring to focal-backports. ie. it’s a mechanism to get backported (from subsequent releases) software into your system meaning you have later (or newer) software, but the security & other support that exists for them only applies to users of subsequent releases (so you’re not getting that benefit until you release-upgrade to a later release).
If you want to get the latest software available then use it; if you’re happy with the software released for Ubuntu/Lubuntu 20.04 LTS with full security support; don’t include it.
I’ll provide a link if you need more information - UbuntuBackports - Community Help Wiki A key phrase found in that document is
Unlike the packages released with Ubuntu, Backports do not come with any security support guarantee.