Wi-Fi degrades speed based on walls and distance. Plug your computer directly into the router via a Cat6 Ethernet cable.
There is a second, legitimate occurrence of "100.100" that is not a speed at all. The IP range is reserved for specific VPN protocols (like WireGuard or legacy Cisco VPNs). Occasionally, a misconfigured speed testing tool will attempt to resolve a hostname to 100.100.x.x and mislabel the latency as "Speed 100.100." If you see this, you are looking at an IP address, not bandwidth.