Hello @RolfF

It's a design mistake.
It is a basic mistake to add 5V to 3.3V system.
5V enters the RF circuit, causing deterioration or damage.
There are many cases where ATOM has already broken.
M5Stack Community
Short Wifi effective range and IO0=3.9V issue with Lite and Matrix : About a year ago
M5Stack Community
New CH552 firmware for Short-Wifi-Issue of M5Atom/Stick/TimerCAM/etc. : About 9 months ago
Bugs and measures for M5Stack ATOM : 2021.10.10
How to not change FW.
Other measures : Low the voltage of GPIO_0.
The voltage on GPIO_0 decreases and the transmit power increases.