There is a simple workaround to post Instagram stories without opening the main Instagram app. For this purpose, users will need to download the Threads from Instagram app from Google Play Store or App Store. This app quickly lets you post photos or videos on Instagram Stories without having to go into the main app.

source https://gadgets.ndtv.com/how-to/features/instagram-stories-posting-without-opening-app-how-to-steps-guide-2399671#rss-gadgets-all