Indeed... my semi-D in Watten Estates had interior walls that were all brick and plaster. Wifi signal propagation between floors was hopeless... had to have a wifi access point on each floor. 2.4 GHz could make it through about one wall.
Now, if you live in a modern
condo, the walls probably aren't built that way, but chances are good that metal is present if you have a two floor setup, or perhaps has metal studs in the walls... which shouldn't matter too much.
Ethernet over powerline adapters worked great for me... YMMV... because they worked like crap in my house here in the USA. And yes, 2.4 is more penetrating, longer wavelength.