In a medium bowl, combine baking soda in the sour cream. Set aside to allow the baking soda to dissolve.
Coat the inside of a 6-cup bundt pan with non-stick spray.
Using an electric mixer, cream the butter with the sugar in a large bowl until thoroughly combined. Add the eggs one at a time and beat until uniform.
Add the baking powder, bananas and vanilla extract to the sour cream mixture and stir to combine, then fold into the mixing bowl with butter/sugar mixture.
Add the flour and stir until just combined. Do not overmix.
Pour batter into the bundt pan and cover loosely with foil--do not seal.
Put 1 1/2 cups of water and the trivet in the Instant Pot. Carefully lower the bundt pan onto the trivet.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- buttons and program the Instant Pot for 45 minutes.
When the time is up, let the pressure naturally release until the pin drops (typically 15-20 minutes), then carefully remove the pan from the Instant Pot and let cool for 5-10 minutes.
Turn out onto a plate while still warm.
Notes
*If your Instant Pot does not have a MANUAL function, use the Pressure Cook function.