This could be attached to a wifi type app you've got turned on / open.
Look in your multitasking by pressing the key on the Left hand side of your navigation bar and close one at a time to see if the icon goes off in your status bar so you'll then know which app is driving it.
I'll keep looking to see if I can see if its also a system icon.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.
It's the cast icon, I'm not aure why it would appear on the status bar, but it is the icon that comes up streaming apps when there's a device to cast to.
Are you currently casting to anything? E.g. Chromecast, TV or Bluetooth Headphones
Do you have any apps open that can detect casting? E.g YouTube, Netflix, etc.
This usualy means that you are casting ypur device's screen to another screen like PC, TV, Chromecast.
It can also appear when you are running an app that can overlay another app. Just check the apps running in the backgroud