I enjoy using the Itch launcher to download and play games. However, now and then there is a game I can't download through Itch (usually because of how/where the game is hosted). I can independently download the game just fine, and I can move the game folder into Itch's downloads directory (%appdata%\itch\apps\), but I can't seem to find a way to then point the launcher to the executable.

I'd gotten around the "can't download" issue before only when a game was originally hosted on Itch.io (or somewhere compatible with the launcher) and only later couldn't be downloaded directly, in which case I would just replace the existing folder contents with the new files. I'm unable to do even that with a totally fresh install, though.