Hey there!
Thanks for using Apple Support Communities. We're happy to help troubleshoot Wi-Fi on iOS 14.
Does this occur in any wi-fi location, or at home? If your router supports it, you might have private addresses enabled on your network. If so, try disabling it before testing again: Use private Wi-Fi addresses in iOS 14, iPadOS 14, and watchOS 7 - Apple Support
Test to see if the issue is resolved by changing the channel that your router uses: Recommended settings for Wi-Fi routers and access points - Apple Support
Also, let us know if Wi-Fi speeds improve with Bluetooth disabled from the Settings menu.
We look forward to hearing back from you! Take care.