I just tried it and as i expected it doesn't work for me. If you have a look on the schematics you can see that the 3.3V are only used as a logic level for the STLink. No modules on board of the Portenta uses this 3.3V.
So if you put 3.3V on any pin the only thing changes is that your STLink now knows the logic level.
But nice that this worked for you 