Official comment
You can do it in ONTRAPORT with either some JavaScript code or, sometimes, features of the other form processor. This option is not available in either ONTRApages Free or ONTRApages Premium.
To pass the data via the URL open your ONTRAform for editing in ONTRAPORT. Click on the Smart Form block to edit it, and click the "Form Settings" button. At the very bottom of the form settings dialog is a checkbox for "Pass CGI variables to Landing/Thank You page". When checked, this will populate the URL with the values your contact enters.
This article in the Gleam Forms knowledge base details how to use the CGI variables passed to it: https://gleam.io/docs/advanced/prefill
If you have ONTRApages Premium you could use the Zapier integration to send data from ONTRApages to Gleam (Pro plan and above).