I can add to the list of shops where this is not working. I set up PayPal Express and Venmo is showing up as an icon in the accepted payments in the footer of my store but it is not available as a payment option at checkout. I was hoping to find a solution here, but all I can do is chime in to report the same issue.
Venmo has a number of buyer-based restrictions. Currently, buyers who do not meet these requirements won’t be able to see the option to pay with Venmo: )
Buyer must be located in the United States
The shop must be located in the United States
Must use a mobile device with the latest version of the Venmo app installed
Must have online purchases enabled within the app!
Venmo will show up now in checkout