Hi babua123,
welcome to the Apple (user-to-user) Community!
Re: How can I uninstall Iriun :
Seems Iriun is an app, (one that also needs a driver to use an Android phone as a webcam).
Best to try using the uninstaller from the developer.
If needed: How to contact an app developer - Apple Support
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Re: "... and stop it from blocking my default cam?"
Head pointer accessibility feature: Choose Apple menu > System Settings, then choose Accessibility in the sidebar. (You may need to scroll down.) Choose Pointer Control, choose the info button next to “Head pointer”, choose Camera Options, then choose a camera.
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Trouble-shooting if needed:
You can decide which apps are allowed to use the default camera on your Mac:
Note: FaceTime, Photo Booth, and other apps that come with your Mac automatically have
access—you don’t need to give them permission.
See how to: Control access to the camera.
Eg: says:
In System Settings > Privacy & Security (You may need to scroll down.) >
On the right choose "Camera"
Turn access to the camera on or off for each app in the list.
The list shows apps you’ve installed that have asked to use the camera.
If there are no apps in the list, you haven’t installed an app that uses the camera.
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If you use Screen Time:
make sure your camera is turned on and apps that use the camera have time available.
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In Safari, to allow a website to use the camera,
choose Safari > Settings > choose Websites > then select Camera.
All the best :-)