My sympathies to the OP, I find it quite unfair that a Cubase 10 Elements license does not allow Cubase SE3 to run, unless of course there’s some technical reason to do with the Soft eLicenser (SE3 used what was then still known as Synchrosoft).
What I can tell you (I have actually done this, so I’m 100% sure it works) is that it is possible to run Cubase SE3 on a Windows 10 machine that has a Cubase Artist 10 license, however that also requires you to purchase a Steinberg USB eLicenser (physical copy protection device).
Running such old software is always problematic however, so what I did was install Cubase SE3 on an old Windows XP machine, then zip up the program folder and copy it across to the Windows 10 machine, unzip and run from there (but with the Cubase SE3.exe in XP compatibility mode). It works well enough to load and save .ALL files to .cpr