The LMDE on my other desktop is based on Debian 10.Hmmm, I've fired up my laptop and on Debian 10, I've got cmake v3.13 installed..
LMDE 4 "Debbie" is supposedly Debian 10 based, so the package versions should pretty much match up with what I have installed.
Which version of Debian is your LMDE based on? For it to be using 3.10 of cmake, it can't be Debian 10?!
When you update it, are there any held packages that require a dist-upgrade in order to install?
That's the only other possible cause of discrepancy I can think of offhand.......
Looking at the top of CMakelists.txt in the root of the xiphos directory - it clearly specifies that cmake version 3.11 or greater should be used and that earlier versions are NOT supported.
BUT in the two lines at the top of the file (after all of the initial comments) - you could TRY changing the occurrences of 3.11 to 3.10 and then go back into the build directory and run the cmake command from my previous two posts.
But whether it will work or not will be a bit of a crap-shoot. I'm assuming that their CMakelists.txt file must be using some functionality that is specific to 3.11.
If that doesn't work, then there's no much hope of building xiphos on your installation of LMDE.
I'm trying to follow the instructions you have given me for Elementary OS which is based on Ubuntu 20.04 Focal Fossa.
Once I get that right and Xiphos installed I plan to follow your instructions all over again to get Xiphos installed on LMDE.
If I have to I'll install LMDE over Elementary.
I'll try installing version CMake 3.11 on Elementary and see if that helps and try your instructions again.