Hello! Sophia here from Shopify.
Since Privy is a third-party app, I recommend contacting Privy directly for guidance on removing any leftover code from your theme if you've already uninstalled the app but the popup remains. You can find their contact information on their Shopify App Store page here: Privy ‑ Pop Ups, Email, & SMS. They currently have a phone number and email address listed. Alternatively, you can click Get support on the same page to connect your support request to your Shopify store.
If the popup doesn't include the Privy logo or you've otherwise determined that it isn't coming from that app, please let me know the name of your theme and whether you're using any other apps that might offer a popup so we can find out where it's coming from. Feel free to share your store link here as well so that myself or others in the community can take a look with you. Thanks!