I can see what looks like a Microchip PIC uP and a WS2812 LED, but are you sure it’s all SELV 5V? (i.e. uses batteries or a fully isolated external PSU).
A capacitive dropper PSU can run 5V uP, but touch any part (including “0V”) and you’ll get a shock.
There’s what looks like a bridge rectifier bottom left, and although there’s no magnetics on the PCB for a boost/ buck chip, many current devices run at low voltage, BUT the PSU is still referenced to mains voltage.
Relays are bulky, but can give galvanic isolation. Optocouplers can also work, but in both cases you need to know if the input is positive or negative logic (i.e. pull high or pull low).
For hints on reverse engineering (and ubiquitous BigClive link):