What’s the best way to connect a PC through thick walls?

If it’s practical, a long Ethernet cable is still the most reliable solution. Otherwise, look for a WiFi 6 or WiFi 7 adapter with proper external antennas rather than a tiny USB dongle. The adapter should be compatible with your router, but newer standards alone won’t overcome poor antenna placement or a difficult wall layout.

Before replacing the card, try using the router’s 2.4 GHz network. It’s slower than 5 or 6 GHz, but it generally travels through walls better. If your router combines the bands under one network name, you may need to separate them or manually choose 2.4 GHz. Also, try a 40 MHz channel width on 2.4 GHz for a reasonable balance of speed and stability.

Powerline adapters are another renter-friendly option: one unit connects to the router, and the other goes near the PC. You can use Ethernet from the second unit or use it as a wireless access point. Just be aware that performance depends heavily on the building’s electrical wiring; some people get excellent speeds, while others see results closer to 30 Mbps.

A mesh WiFi system is probably the most convenient wireless fix. Put one node near the router and another closer to the PC, then connect the PC to the nearby node with Ethernet if possible. That gives the desktop a stronger local connection without needing to run a long cable through the flat.

The antennas may be more important than the WiFi card itself. A PCIe adapter with large external antennas, or a separate antenna that can be positioned higher and away from the back of the PC, can make a noticeable difference. Since your phone and laptop work well in the same area, improving the desktop’s antenna placement is worth trying first.