I have same problem since first upgrade to iOS14.x on iPhone SE, iPhone 11 Pro Max and iPhone SE 2020. On my windows laptop I have no problem, the wifi works fine on TV and XBox as well. It is clearly an iOS 14 problem that apple didn't solve, or they don't want to solve due to some security or compatibility issues (ı guess). But at least I expect a kind of official explanation why this is happening, is it spcific to some router models only...etc.

Same problem on all iOS14.x devices https://developer.apple.com/forums/thread/651079?page=1#654065022