The first thought is often the right one.
The sensor fits exactly into a matchbox, a small magnet holds it on the surface and the cable disappears behind the kitchen cupboard. The ESP32 is hidden on top of the kitchen cabinet and controls a relay for a light. I had a Zigbee PIR motion detector and some ZigBee switches in the kitchen. However, the ZigBee network is anything but stable. Despite all my efforts (ZHA, or Zigbee2MQTT, firmware update, WLAN/ZigBee channels cleanly separated, etc.), I didn't feel like wasting any more time and am now gradually replacing all the problem components with Esphome devices (ESP32, ESP8266, Shellys, Sonoffs, etc.). WLAN just runs smoothly.
p.s. the apparent cylinder is a small enamel plate, and was created when photographing at an oblique angle