OK, I got this working. I couldn't find the documentation for them, but it looks like the FunctionResourceBoxes (the boxes which say WolframModel) install specific versions of libraries. The interpreter paclet in the given version is somehow broken on Raspberry, but you can use the one which comes with the installation. To do that, just replace the FunctionResourceBox by a plain call to WolframModel, and remove the broken "Interpreter" paclet from .Mathematica/Paclets/Repository.

But there is another problem: WolframModel is defined in the paclet "SetReplace", which you can download from here: https://github.com/maxitg/SetReplace/releases . But if you install it, you get a warning that it is not compatible with your system. This seems only half true, as it brings a binary library which looks as if it does not build on 32 bit systems. But the binary library seems mostly to be needed for peformance reasons, and it looks like most (if not all) things can run without it. Just edit the file .Mathematica/Paclets/Repository/SetReplace-0.3.39/PacletInfo.m and add "Linux-ARM" to the list of SystemIDs (you are allowed to do that, because it's a separate paclet under MIT license), restart Mathematica, and run

<< SetReplace`

if you replaced the FunctionResourceBoxes by a plain call to WolframModel, you should be able to run the notbook now. Some operations take while though, but I guess that's to be expected when trying to run a universe on a Raspberry, single-threaded and without performace optimizations. But it's still fun :-)

Update: I'm not sure anymore if it's enough to edit the PacletInfo.m of the installed package (as I have trouble reproducing that). I also downloaded the source for SetReplace and tried to build it. The build fails (some 32 bit vs 64 bit issue) but it still creates a package. If I modify the PacletInfo.m in the source before building, i get a working package. Perhaps I got confused by the many SetReplace versions and the order in which I tried things. At least it's doable.