'pkcon install' only installs packages whose arch matches that of the OS:

https://github.com/hughsie/PackageKit/commit/e4b24fe79d773bd624d9d45cfcd312fe3a16a497

It's understandable that this behaviour is useful for preventing accidental installation of packages not designed for an OS's architecture. However, there are plenty of 32-bit applications & libraries that are useful on 64-bit systems, so the user interface of pkcon for installing packages of different arches should be easy to use & understand.

However, pkcon's documentation is lacking in instructions of how to do this. pkcon's manpage doesn't say how, and neither does PackageKit's webpage (https://www.freedesktop.org/software/PackageKit/), at least not explicitly. Because of this, for the longest time I have relied on using dnf to install 32-bit packages.

I found the solution only after many desperate web searches, which led me to the above git commit, and to the "How to Use PackageKit" page, which just so happened to show in passing that filters can be negated with the ~ character, a fairly useful feature not at all mentioned by pkcon's manpage. From this, I finally realized that the way to install a package of a different arch than the OS is with 'pkcon --filter ~arch install <package name>'.

There is nothing objectively wrong with needing those extra arguments, but without any documentation about it, it takes more knowledge than is reasonably expected from an end-user not familiar with pkcon's/PackageKit's internals to arrive at that solution.

What makes this even more confusing is that 'pkcon search' does show packages of a different arch than the OS. A typical reaction to this is to assume that anything found by 'pkcon search', regardless of its arch, can be installed by 'pkcon install', but that is not the case.

If pkcon is intended as a user-space utility rather than just a backend to GUI tools, its documentation should be improved accordingly.