The purpose of selecting a board type in Blynk Legacy was to change the list of analog and digital pins available in the app, and to ensure that these mapped to the correct hardware pins on the device when using analog or digital pins (as opposed to virtual pins).
It also restricted the number of virtual pins available for boards that had 8-bit processors and limited memory/processing power.
In Blynk IoT only virtual pins were available initially, and the numbers of datastreams is limited by your plan type rather than the selected board type.
If you use virtual pins then it makes no difference what hardware you are using, you handle the digitalWrites and digitalReads yourself.
If you want to use analog or digital pins in your Blynk IoT datastreams then it’s currently anybody’s guess how this is meant to work, as discussed here…
Pete.