No; definitely not easily anyway.
Ubuntu releases are easily dated because of the year.month format used, and if you look you'll note debian release don't match up (eg. there was no debian release in 2018 near 18.04; debian releases are usually in odd years and when ready so the software never actually aligns. Many debian-stable packages are behind Ubuntu ones (as Ubuntu usually takes from debian-testing/sid so is ahead of debian-stable), but not always as many ubuntu packages push code upstream to debian to save work... The two don't align perfectly at all - so not it's not really possible.
If you do what you're asking, you'll soon find yourself in dep-hell (compare key packages in packages.debian.org to packages.ubuntu.com and you'll find it's rare for debian to match ubuntu) See https://wiki.debian.org/DontBreakDebian provided by @DK Bose
Debian packagers make different choices to Ubuntu packagers; those decisions cause issues you'll discover if you tried what you're thinking. I'm involved with Lubuntu (LXQt) which actually is pretty close to Debian (comparing my Lubuntu 20.04 to debian bullseye/sid [albeit superficially inaccurate]), but we use
xfwm4, we use ..... - ie. differences are made & these show in packages (esp. deps) because of our choices in other packages etc.... they are different, to assume they aren't leads to problems..)
There are instances were the Debian packager is the same person as the Ubuntu packager (I see Debian packaging discussions occasionally mentioned in Ubuntu flavor (note: I'm found in more than just Lubuntu) [irc] rooms; pushing it upstream to debian-sid so it'll flow (or can be pulled) into Ubuntu as well), but even if the it's same person, different rules may be used due to the different environments & decisions made by teams (eg. my prior example of dm/wm used by LXQt Debian vs Ubuntu)
Another problem - even if you do get a Debian/Ubuntu system to install (rather possible depending on what you build I believe) your upgrade path should be taken as being none-possible & start again. ie. I very much doubt
do-release-upgrade will work with Ubuntu in performing the upgrade; and debian's upgrade tools will likely fail too.
This question was asked first on Ask Ubuntu, my comments made there I've copied here. Sorry this isn't really an answer; more thoughts expressed with some skipped, and very minor editing only