Apparently it's a pretty common issue for people using this board. There are a couple of solutions here that I will try: https://github.com/IOT-MCU/ESP-01S-Relay-v4.0/issues/1
The most non invasive one with Tasmoto firmware didn't work in my case. So I will try another pin and if that fails, bite the bullet and introduce a capacitor.
The TP4056 is a battery charger, not a voltage regulator. It cannot be used to supply power to a device like an Arduino. It is designed for charging the Lithium Ion battery from a 5V (e.g., USB) source.
By trying to use it as a power supply you're asking for trouble. It thinks it's trying to charge a battery (from a 3.7V nominal source) and will be doing ...
You cannot find a tutorial for controlling neopixel strips with a relay, because that just does not make any sense. You don't need a relay to control the strip.
The Neopixels consist not only of the LEDs themselves, but also of one LED driver chip per LED (WS2811 and it's siblings). These driver chips control the LEDs based on the data, that you send through ...
This can also be a power shortage as there will be a drop when the relays turn on, depending on you psu it might not respond quick enough, so you get a brown out. I added a bit 4700uF cap on the psu power line to the arduino.