Make Nextcloud client login automatically with KDE autologin and an empty kwallet password

I would like to auto login to KDE since my computer drive is encrypted. The expressions

displayManager.autoLogin.enable = true;
displayManager.autoLogin.user = "tiez";

faciliate the auto login but then my kwallet is not opened automatically. The wallet already has an empty password and if I start KWalletManager and click “Open”, it opens without entering any password. Still, the nextcloud client does not “realize” this and asks me to login. The nextcloud client is in my KDE Autostart. When logging in with a password, pam(?) seems to open the kwallet automatically and nextcloud logs in, too.

I searched for 1-2 h and couldn’t make it work. Some guides suggest changing pam.d configuration files but I couldn’t test these since AFAICS this is not possible in NixOS.<name>.enableKwallet did not solve the problem.

Anyone got this working properly without wrapper bash scripts which first open the kwallet and then start nextcloud?