Hello, moon-daisy.
Thank you for posting in Apple Support Communities. We understand that you’ve been experiencing an issue where the content is blurry when posting photos or videos to Instagram Stories. We may have a few suggestions that will help.
First, it’s always a best practice to ensure that your iPhone and the Instagram app are both updated.Â
Update your iPhone, iPad, or iPod touch - Apple Support
How to manually update apps on your Apple device - Apple Support
The camera on your iPhone 12 Pro Max the strongest available with an Apple product. If you’re capturing photos and/or videos using the Camera app on your iPhone and the content is only blurry after you post to Instagram make sure that you’re posting when you have a strong and steady internet connection. Usually, Wi-Fi is usually best.Â
You might also look at your Camera settings on your iPhone. Do you have High Efficiency or Most Compatible selected? Try switching to the other and capture a photo or video to upload to Instagram and test. Does it change the quality? If not, try disabling Apple ProRAW, too. Instagram may be compressing or adjusting the parameters of your photos and videos when you post.Â
These article will help:
About Apple ProRAW - Apple Support
Using HEIF or HEVC media on Apple devices - Apple Support
If adjusting your Camera settings doesn’t work, try capturing a video using the embedded camera in the Instagram app.
Still no luck? I may be time to reach out to Instagram for help:
Instagram Help Center
Warmest Regards.