Q: 5G wifi connection on my iPhone underperforms

Hi Lsum990,

Thanks for checking out the Apple Support Communities! I understand you're having trouble with your connection speed on your iPhone when you connect to Wi-Fi. I use my iPhone with my home Wi-Fi network all the time to download movies and music so I know having a fast connection is important. I'm happy to offer some suggestions to help you get this working. 

The first thing that I recommend doing is taking a look at the steps in the article below. Even though you can connect, the steps here are still good to go over when you're having trouble with connection, specifically the section regarding resetting your network settings. 

Still Can't Connect?

Reset your Network Settings. Tap Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before.

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

Since you're having trouble with the Wi-Fi on your iPhone, there may be sources of potential interference causing connection issues. I've provided an article below to help you determine if this is happening with your current setup. Also, depending on your current network settings, you may need to make some adjustments for maximum performance. Take a look at the information here for the suggested Wi-Fi settings for iOS devices:

Recommended settings for Wi-Fi routers and access points

Potential sources of Wi-Fi and Bluetooth interference

Cheers!