Thanks. The S3 Zero is a commercial small module and I assume the regulator has a correct spec.
I have solved the problem by
1. introducing a few seconds delay between turning on wifi and initialising ESP-NOW
2. moving the decoupling capacitor from the 5V pin to the 3V3 pin
Later I replaced the ...

How reliable is the reset reason that you can obtain from the ESP32?
I ask because I have an ESP32-S3 supermini that is resetting itself intermittently. It is in a portable medical device that reads 3 sensors regularly. To save power it only turns on the WiFi every 5 minutes, transmits the data over ...

just for completeness ... I've now got the second supermini and it's even worse. After any upload, even blink without Serial.begin(), it refuses further ones until put into upload mode. I'm now using a Raspberry Pi Zero which is much less hassle.

Thanks for the suggestions. I don't have a second board to try, but I've got one on order (which I'm kind-of regretting).
The Arduino IDE board manager shows the following installed
Arduino ESP32 Boards by Arduino 2.0.13 installed
esp32 by Expressif Systems 2.0.15 installed
there are no later ...

I'm an amateur Arduino user who wants to upgrade to something with more RAM. The ESP32-C3 supermini looked good because its small size fits on a breadboard. However, like many people, I have found it very tricky to use. I now have a puzzling situation with a very simple sketch - the basic blink in ...