Kepware’s client has long been broken such that you need to configure Ignition’s OPC UA server to allow unsecured connections.
In the Ignition OPC UA Server settings area you can set the Security Policies to None, Basic256Sha256. You’ll also have to set the Bind Address to 0.0.0.0 if Kepware is running on another machine because Ignition’s server only listens on localhost by default. These changes require a restart to take effect.