Is this another one of those Android 11 problems?
I try to use the extension @TIMAI2 made but when I want to scan something I get
Permission Denial: starting Intent { act=com.google.zxing.client.android.SCAN cmp=com.sophos.smsec/com.google.zxing.client.android.CaptureActivity } from ProcessRecord{6701508 18885:edu.mit.appinventor.aicompanion3/u0a366} (pid=18885, uid=10366) not exported from uid 10304
when I use DoScan.
Did I make a scanner extension ?
This one
I wanted to make an app to decode my own covid vaccine qr code.
I finished my code vaccine qr extension 
Great. Do you have any idea why i get this error? I guess i would get it with your extension also.
Hmm. This seems specific to the BarcodeScanner and not Tim's extension.
Android 11 introduces a new <queries> element to the manifest and in some instances you can only launch activities if the corresponding information is present in that element. This is the same reason that the speech recognizer is broken on Android 11. There is a pending pull request that contains a fix for this and generally makes adding content to the <queries> tag available to components (and extensions).
Yes i know. Android 11 made a lot of things very difficult. 
Well, the theory behind the change is to prevent apps from fingerprinting you as a user. For example, if we assume that the installation of apps is orthogonal (there's no relationship between whether you'd install an app A versus app B), then you could test for the presence of 33 different apps and you could uniquely identify a person (2^33 is roughly 8 billion combinations).
Of course, people who aren't interested in tracking users are also affected (e.g., we really don't care what you use App Inventor for, and we don't embed any tracking information in the applications people build since we're a research project at a nonprofit university). Therefore, you get to pay the penalty for other people's greed.
Note: We'll fix this in the change that addresses the SpeechRecognizer issue as well.