Diagnosis
This is a known issue with interference on the 2.4GHz band or a weak signal on the 5GHz band due to the projector's internal antenna placement. Metal components inside the chassis can cause signal blockage.
How to Fix It
Force the projector to connect to your 5GHz network. Go to Settings > Network & Internet > Wi-Fi. Select your network, then 'Forget'. Re-select it. If both bands share a name (SSID), split them into separate networks on your router (e.g., MyNetwork_5G). Connect explicitly to the 5GHz one. In Wi-Fi advanced settings, set 'Wi-Fi frequency band' to '5GHz preferred'.
If That Didn't Work
Use a wired Ethernet connection. The Horizon Ultra has a 100/1000 Mbps LAN port. For a permanent setup, this is the most reliable solution. For a temporary test, a USB-C to Ethernet adapter also works on the USB 3.0 port.
Heads Up
The projector's Wi-Fi performance is highly directional. The optimal antenna orientation is with the projector's rear panel (where the ports are) facing generally toward your router.