こんにちは。
以下のリンクは確認されましたか?
「Microsoft Flight Simulator X: Steam Edition」
"Steam initialisation failed, steam must be running to play?"
https://steamcommunity.com/app/314160/discussions/0/622954747290713456/
リンク先に、
that is the correct procedure, right click steam and run steam as administrator, that should allow FSX to inherit the admin rights it needs
他にも同じようなアドバイスがあります。
I found another solution, this is for users that already required User Account Control (UAC for short - the blue and yellow shield icon) to load the game, and you could play fsx until suddenly UAC required a password. To fix this, you simply need to switch
your user to administrator. Clicking "run as administrator" won't work if it already requires administrator password.
If you are confused on how to switch your user account over to an administrator user (In Windows 8 and above, not sure how to below), you must go into PC settings on another user that is already an Administrator, click accounts, other accounts, select your
user, click edit, and finally set your user to administrator.
Hope this helps.
翻訳機能を使用し参考にしてみてください。
管理者としての実行が必要というような内容だと思います。
または、右クリック管理者として実行。