Not that there are no smart plugs available off the shelf, it's just if you want to have a total control over the software - you need to build one for yourself (or, hack an OTS product). The partitions inside the case reflect the dimensions of the used parts. The top cover has a hole for 8mm multicolor led (to indicate IP connection and on/off relay states), and a second smaller hole for microswitch pushbutton for manual on/off/pairing(?). In case you were wondering - 2 relays are needed a for complete power cutoff (both L and N lines); only earth/ground wire remains connected all the time.

Parts used in my design:
PSU: https://aliexpress.com/item/1005010636851659.html
Relays board: https://aliexpress.com/item/1005011743253008.html
SoC board: https://aliexpress.com/item/1005010044041548.html