Does FSX have a demo?

The best you can get is the FSX Demo version, which gives you about 30 minutes of flight.

Can you play FSX with keyboard?

Both FSX and MSFS 2020 can be played using a keyboard and a mouse, if you choose to do so.

How do I add aircraft to FSX Steam Edition?

Starts here10:47How to Install Add-on Aircraft in FSX: Steam Edition – YouTubeYouTube