I’m using just humidity and its working great. I put the sensor away from my sink so it isn’t triggered by washing my hands.

This will only consider you showering if humidity goes 9% above the 1hr average humidity:

You need a ‘Statistics’ Helper, call it “Average Bathroom Humidity” and base it on whatever humidity sensor you have. Make it “average linear” then set Max Age to 1 hour. (leave other options default)

Make this Template Binary Sensor called “Showering”:

{{ (states('sensor.bathroom_sensor_humidity')|float - states('sensor.average_bathroom_humidity')|float) > 9 }}

Multiple waterproof 4k cameras pointed at the inside of your shower from every angle and image recognition by some AI that detects when a naked person enters.

Don’t forget to use Wifi and no firewall

You could use a classic dead man switch: Place several buttons around the whole place - basically everywhere except in the shower. Once you stop pressing any of these buttons for - let’s say - 30 seconds you can assume you’re taking a shower.

Made a flowchart for you:

< Do you feel wet? >  
     |  
     +-- yes --> < are you indoors? >  
     |                |  
     |                +-- yes --> < are you wearing pants? >  
     |                |                      |  
     |                |                      +-- yes --> [ you peed yourself ]  
     |                |                      |  
     |                |                      +-- no --> [ you're taking a shower ]  
     |                |  
     |                +-- no --> [ it's raining ]  
     |  
     +-- no --> [ you are not taking a shower ]