@yeri I have a house with cellar, basement, 1st and 2nd floor. And the floors between those houses are concrete with iron nests in between. A WiFi signal from the basement has a hard time traveling into the 2nd floor, for example.
But somehow Zigbee is super reliable.
The "smart" sockets I have work as repeaters.
On HA's side I have a USB cable, and only then do I have a Zigbee stick. Don't plug the stick in directly, too much computer made RFI. Then one of the older, bulkier smart sockets from IKEA one level above became repeater, automatically. Then another level is the small heating room. And there's another smart plug that controls a "circulation pump". And since 6 months there never was any connection issue, the pump correctly turned on/off by timer. Or via a Zigbee switch on demand. Super reliable for me.