Steam Version - Freeware Addons/downloads

Read these over crefully, I think they work with Steam.

https://flyawaysimulation.com/downloads/search/?q=FSX+steam&cat=

Steam you buy and play mostly on line, FSX Gold was the original version which you but and use on your machine, you own it and can play it anytime you wish without being connected to the net.

See if this helps.

https://support.steampowered.com/kb_article.php?ref=3160-AGCB-2555

If you want to own and play it check on line to see who has one for sale.
They have been discontinued by Microsoft, maybe check ebay.
Be sure to get a key number when buying.

Most, if not all of the FSX addons (thousands) we have here work with the Steam Edition:
https://flyawaysimulation.com/downloads/fsx/

However, the installation directories are a little different.

I can assure you that any aircraft, scenery, or props that you download will work just fine on the Steam Edition of FSX, provided you have some basic common sense and take the time to read the readme files included with downloads. I can help by specifying for you that your FSX install is most likely at "C:\Program Files\Steam\SteamApps\Common\FSX\", unless you chose to either install steam, or FSX, elsewhere. Once you know where to find FSX, just follow the instructions for where to put the various files/folders within.
Example: MOST aircraft are distributed in a .zip format, typically with the primary aircraft files in a folder named for the plane, which will go in the "C:\ProgramFiles\Steam\SteamApps\Common\FSX\SimObjects\Airplanes\", and then may include other folders for Gauges and/or Effects which will be "merged" with those folders under the FSX folder.
Typically, the instructions will tell you NOT to overwrite existing files. I tend to always keep whichever file is newest, and it has served me well. If all else fails, and you are having difficulty with an install, you can always check forums or FAQs. FSX has a huge and knowledgeable user base that tends to go out of its way to help new users.
I do recommend making a back-up of FSX "clean" before you start adding things onto it, because it is potentially possible to break the program if you muddle with the wrong things. It's easiest to just start over than to either try to figure out what you broke, or wait for Steam to either fix it or download it again.