Experiencing the same issue here:
Popup doesn't appear
iPhone 12 Pro Max 14.3 & 14.4 Popup appears
iPhone X 14.2 & 14.4iPad Pro 11" 14.2 & 14.4iPhone Simulators All devices are set to "Allow Apps to Request to Track"
With the iPhone 12 Pro Max, even with this setting enabled, the App doesn't appear within the "Privacy -> Tracking" submenu as it does with the others. To me, it seems like the "Allow" setting is stuck on "Deny" as the toggle seems to have no clear effect.