Two different issues going on. First, you are comparing a string to a boolean. While this can be made to work through forced type coercion, its far better to use explicit comparison. The second and bigger issue is you are telling GenieACS to use stale data for its comparison.
const now = Date.now();
let WANPPPConnection1 = declare("InternetGatewayDevice.WANDevice.1.WANConnectionDevice.1.WANPPPConnection.1.Enable", {value: now}).value[0];
if (WANPPPConnection1) {
let WANPPPConnection1UpTime = declare("InternetGatewayDevice.WANDevice.1.WANConnectionDevice.1.WANPPPConnection.1.Uptime", {value: now}).value[0];
if (WANPPPConnection1UpTime > 0) {
declare("Tags.Ok", null, {value: true});
}
}