I doubt if the 2.94V is a problem. I accidentally just bricked my Portenta again. I hooked up the SCL/SDA of an Arduino Uno to the SCL/SDA at I2C1 on the Portenta breakout board, ran my program and got it back to 2.94V. But I was unable to get connection.
Re-reading my instructions in post #6 of that thread, I moved the dip switches and double-clicked on the breakout board, only then I was able to connect STM32 Cube Programmer. After disconnecting it I could burn the boot loader from the Arduino GUI and everything was good again. I don't know why the dip switches must be used (it was trial and error and there probably is a good reason for it) but in your case, next time it happens try doing the same. I broke and restored my board deliberately several times this way and it has always worked.