@J4n13 8 meters of air is absolutely no problem but I assume there is at least one wall between those points maybe more. WiFi signals lose power when passing through solid objects to the denser the material the greater the loss. If your block has concrete walls you would expect significany sihnal loss. The other issue in flats is while you maybe 8 meters from your router you are quite likely to be the same or less from one or more of your neighbour's routers. it is not unusual to have. 8 or more networks within sufficent range to cause interference in many blocks of flats. Although in theory there are for example 13 channels in the 2.4GHz band only 3 or at most 4 signals can be in range to avoid interference.
The first thing to try is to reboot your hub which will cause it to find the leastcongested channel to use. Secondly ensure the hub is in the best position which is out in the open on a surface so it is above as much furniture, radiators etc as possible. After that you are into needing additional equipment. Sky can supply extdners if you buy their WiFi Max bundle https://www.sky.com/help/articles/sky-wifi-max but there are thirs party equipment you can buy which can be a better fit for your issue.
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
