Hi Instagramvideosbadquality,
Hi. We see that you're experiencing quality issues with videos and stories on Instagram. We will do our best to assist. Do you experience similar issues in other apps such as Camera, Facebook, etc? If it is only happening in Instagram, check for updates by following the steps here: Update apps or use automatic downloads.
Another step is to delete and install the Instagram app. To do so, open the Settings app. Tap General, then tap iPhone Storage. Tap the Instagram app, then tap Offload app. Tap Offload app again. Wait a moment for the app to offload, then tap Reinstall App. If issue continues, we suggest reaching out to Instagram's app support here: Instagram Help Center.
Best regards.