Setting path:
realme UI 7.0 & 6.0 & 5.0 & 4.0 & 3.0: Camera > Switch to front camera > Top right-Settings > Flip selfie/Mirror selfie
realme UI 2.0 & 1.0: Camera > Switch to front camera > Advanced settings > Top right-Settings > Flip selfie
realme UI R & S & T & Go & U Edition: Camera > Switch to front camera > Advanced settings > Top right-Settings > Flip selfie/Mirror selfie