Blue dot in corner of screen

Hi there! That blue dot is voice control. The dot shows up as it's an indicator that an application is using your microphone. If you would like to turn this feature off. You can do this by simply going to Settings > Accessibility > Voice Control.

Here is more information of the feature itself

Use Voice Control to interact with iPhone - Apple Support

I believe this is the "Circle" the user is seeing (Image taken from: Blue Semi Circle at Top Left of Safari wi… - Apple Community)

If this is what the user is indicating, that blue circle then is the iPhone giving the user a heads up that an app (Most likely safari) is using the microphone.

kerty122 Said:

"Blue dot in corner of screen: A blue dot has appeared on the top left corner of my screen and seems to only appear on safari. There are no answers online as it is not the voice control (this has never seen set up on this phone). It is driving my nuts, please let me know what it is and how I can stop it."

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Start with a Screenshot:

See what happens when you take a screenshot. View the screenshot in the Photos app. Does the dot show up in the screenshot? If so, then it is the app itself giving you the issue (so, check for updates). If not, then you may have to restore to factory settings (more on that after you reply).