You don’t need to upload sketches to the Pi.
Install the Blynk IoT contrib from the Node-Red palette.
In Blynk web console create a template, with the virtual datastreams you need, then create a device from that template.
This will give you your template ID and auth token which you use to create a connection in the Node-Red contrib.
You will use the Blynk IoT Write node to write data to the virtual datastream(s) that you’ve created. This can be handled dynamically by specifying the datastream in the message, or in a static way with the datastream defined in the node. The message payload needs to contain the single data value you want to send to Blynk.
This topic explains a bit more. It was originally written for Blynk IoT, but the last post covers some of the changes with Blynk IoT, although the basic principals are the same…
Pete.