I see lsb_release is mentioned below.
https://www.ionos.com/digitalguide/server/know-how/how-to-check-debian-version/
Unfortunately, it may not work on all Debian based systems; for example, on a stock Ubuntu 20.04.2, it returns the following:
$ lsb_release
No LSB modules are available.
Is there any other way for me to find out which version of Debian my current Ubuntu installation is based on?
I suppose you could search for /etc/debian_version, even display it to get your answer.
cat /etc/debian_version
On Debian and Ubuntu (and maybe derivative) systems, /etc/debian_version exists. Looking in /etc/apt/sources.list should show you where the packages were installed from.
It is possible that someone installed the system and then later completely changed /etc/apt/sources.list (which would most likely break the system at next upgrade, but…). In this case you could look at where specific installed packages were obtained from with:
$ apt policy <packagename>
The proper way however is for package lsb-release to be installed so that the command you used gives proper output.
lsb_release -a. – user68186 Feb 06 '21 at 16:43No LSB modules are available.on stock Ubuntu 20.04.2. – Levente Feb 06 '21 at 17:42