I got it working somehow several minutes ago. I redid the rAthena.sln step, open it with Microsoft Visual Studio, then clean and build it again. I repatched the client I'm using (2020-04-01b) with NEMO, applying only the recommended setting and the zoom out patch.
As I was using the empty new.grf while tinkering for the solution, everything were in gibberish. I switched to the custom grf I made previously, but somehow the items are still gibberish. The topic is solved, for me at least.
