Proximity sensor is not working

Realme has a page dedicated to issues with the proximity sensor that's worth a read.

Why the proximity sensor not working - Official realme Support

Their advice comes down to four suggestions.

1. 1. Screen protector or case: try removing it and see if that helps
2. 2. Clean the screen
3. 3. Run the diagnostic test
4. 4. Try updating the phone to the latest version

If none of that helps, they say it's time to send it in for repair. However, there's a guy with a TikTok video showing how you would remove the motherboard and clean the back side of the screen along with the front of the sensors themselves to get the proximity sensor working again.

Realme 6 Sensor Repair and Troubleshooting Guide - TikTok

I don't speak the language used in the video so I don't know what they're saying, but the basics are pretty self-evident regarding what they're doing.

Here's a picture of the motherboard with the proximity sensor outlined in red.

This guide shows you exactly how to remove the motherboard if you want to try the cleaning as outlined in the video.

Manuales / Realme 6 / Base plate - Nadie Me Llama Gallina

According to the video, you also have to remove the LCD from the midframe. Nadie me Llama Gallina doesn't have a guide for that, but this YouTube video shows you the process.

Realme 6 Screen Replacement - YouTube

If you do all that and it still doesn't work, then it's probably a hardware issue. Unfortunately, being mounted on the motherboard means you'd have to get professional repair to fix it; either that, or replace the motherboard.