How is it possible to add a package to the board, without being on the schematic (e.g. a heat sink)?
I do not think that is possible or needed. Why would you not want to have a heatsink in a schematic?
I mean a heat-sink can make sense to put also on the schematics (whats the symbol of a heat-sink?), since it often has holes connecting different nets. But e.g. a logo would in my opinion make no sense to put on the schematic.
To me, I don’t see an issue with a requirement for polygon to have some representation in the schematic. Example above is a kludge because you have to pretend you’re a manufacturer, enter fake MPN, etc, but, what’s on schematic does not have to be connected anywhere.
The main issue, as I see it, is a number of steps needed (many extraneous) to create an one-time or custom object that is an embellishment or self-made part or design.
That is exactly what I was doing as workaround.
For mechanical parts without any electrical connection such as light pipes, there’s the “Mechanical part” entity.
For heat sinks, I’d recommend creating a dedicated symbol/unit/entity.
For logos, well, why not just have them on the board as a polygon?
To properly address the issue of placing purely graphical things like logos and such on the board, we now have Decals: https://github.com/horizon-eda/horizon/commit/d2e88d71601604c82a7ba680fe3da3dfe694ead1