I did not come across that page. I dug into the big user manual, and did not find a page size limit noted there.
If I can get my building department to accept 18" x 24" sheets, this may work. They require ¼" scale for most building sheets, and this house is small enough that it will just fit. Can you comment on any not obvious limitations in Home Designer Architectural 2020 vs. Chief Architect? It appears that the major features are all functional, but there may be some things disabled.
However, the deeper I dig into this, the more convinced I am that I am better off renting Chief Architect Premier for this project. I'm a retired building contractor designing a small retirement home, used to drafting my projects on Clearprint with pencil, which I gather is no longer done much. While CAP is overkill in many ways, the power features will make it easier to make a complete professional submittal package. I am building in a 130mph wind, D2 seismic area, and will have a structural engineer involved.