Q: iPhone SE should be 433 Mbps   and receives only 45Mbps why?

Howdy Kazimierz40,

If you're experiencing slower than expected speeds on your iPhone when connected to your Wi-Fi network then your connection may be degraded by any number of potential sources of interference. The article linked below details many typical sources of interference, along with steps for working around or eliminating their effects on your network.

Potential sources of Wi-Fi and Bluetooth interference
https://support.apple.com/en-us/HT201542

Regards!