Hi,
I have checked your code, it appears that the code about the PIO0_26/27 pins configuration, SWM pin routing, I2C1 init is correct.
Pls check if the OD bit is 1 for PIO0_26/27

Secondly, pls connect a pull-up resistor on the PIO0_26/27, as you know that the I2C pins must be open drain.
If you still have issue, pls connect a scope to the PIO0_26/27 and check if there is waveform.
Hope it can help you
BR
XiangJun Rong