It works the same under plasma-login-manager. It’s just a different conf directory.
Place the following file at /etc/sddm.conf.d/zzz-override-cachyos-settings.conf for SDDM or /etc/plasmalogin.conf.d/zzz-override-cachyos-settings.conf for plasma-login-manager.
[Autologin]
Relogin=false
Session=
User=