This may be hard to believe, but it is NOT a bug issue (if it was you would see millions of posts about it); it is something wrong on your phone. So the only way Apple can fix it is to run diagnostics on your phone.
And this is a user-to-user forum, with minimal Apple participation.
For help from other users, start by explaining not working properly.
And not that most Wi-Fi problems after an update are caused by VPN incompatibility, so try deleting any VPN profiles on your phone in Settings/General/VPN & Device Management/VPN.