Run the check
Start the local comparison below and hold up a card with readable text; the left view is CSS-mirrored and the right view is received by a second WebRTC peer in this tab.
In the actual call app, capture your self-view and ask a second participant or second device to capture the received image with consent.
Compare the orientation of the text in those two screenshots before changing any app-specific mirror option.
Official reference: Zoom Mirror my video setting
Official reference: WebRTC local peer example
Compare self-view with a receiving peer
Hold up a card with readable text. The left pane mirrors your preview. The right pane shows video received by a second WebRTC peer in this tab.
Your call app can apply different processing. For that app, compare its self-view with a second participant or device in the same call. Ask permission before saving another person’s view.
Read the result
If only your self-view is reversed, the transmitted picture may still be normal; the second device's capture is the deciding evidence for that app.
Limits and next step
The receiving peer below runs in this tab, not in a separate call app. That app may apply different processing.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.