[WI-FI] Weak internet connection in the different room from the router

Hello, I have big problem because I have very weak (wi-fi) internet connection in the bedroom on iPhone 11. version 14.4.2

My router is located in the different room (about 8-9 meters)

Websites load very slow and sometimes breaks internet connection. What could be problem and how can I debug better this problem? Do you use any software for debugging?

I have different iPhone X, MacBook Pro 2018, iPad Pro 12.9 and those devices don't have this problem.