Merge tags in multistep Gravity Form?

This is possible with Live Merge Tags, a feature of Gravity Forms Populate Anything.

If you’re looking to get your hands dirty with some code, Gravity Forms has an example of how this might work with a snippet on their docs for the gform_pre_render filter:

https://docs.gravityforms.com/gform_pre_render/#3-populate-field-with-values-from-earlier-page