Cannot find tags under MQTT Engine?

I verified that Edit->Find/Replace in Ignition Designer will find tags eg. GatewayAddress under System.

But, it seems limited to matching the leaf nodes in your tag hierarchy. I tested several cases with no success.

Nothing I type in for Tag Path in Tag Browser Search does anything.

If I have 1000 (or 1 million) different devices with different serial numbers, how can I find the
tag “X” for one of them?

Thank you for any help.