You have to add a line to the /etc/pam.d file for your greeter for KDE’s wallet. The arch wiki page for the KDE wallet should have the line(s) you need

Do you have your wifi password saved in your KDE wallet?

There is an option to not save your wifi password using the wallet, otherwise you will be prompted at startup as soon as it attempts to connect to wifi.

My solution: remove the password or make it blank (I forget which). No more prompting at login.

My whole drive is encrypted, and my wallet only has wifi passwords, so there's no harm.

If you want your wallet to unlock automatically anyway without any interaction, just remove the password from the wallet. As long as your disk is encrypted, there is not much of a security impact.

I fucking hate the KDE wallet popups!!!!!!!!!!!!!!!!!!

I'm a long time Linux user, and I fucking hate the daily popups. I somehow got them to go away on one of my computers.

I installed Linux on the family laptop, and wife took the laptop away from the house to use it and she couldn't get access to the WiFi, I had no idea what was wrong on her end when she called -- I thought maybe the WiFi chip in the laptop was too outdated for new routers. Anyways, I spent a lot of time for an evening for her that turned out of bust because of the annoying popup.