Just doing the math, it's obvious that your shower is putting water into your septic tank faster than it's flowing out into your leach field.
Also, the static level in your tank is too high.
Something may be blocking the outflow pipe from your tank.
I'd say it's time to call in a professional.
JMHO

Could be a problem in the leach field or pipes from the tank to the field.

If you have a recent septic tank it might (should) have a filter at the tank output too keep solids from getting into the leach field.

When those filters clog they restrict the water flow out of the tank and water can (will) backup into the home if the problem is not corrected.

Those filters should be accessible through the cover at the tank output end and are usually attacked to a piece of PVC so they can be removed and cleaned. You can clean it yourself or call the septic company.

Whatever the problem it must resolved cause replacing leach fields is expensive and you have to have the square footage available for a new field.

Maybe taking shorter showers will help.

Its simple something is blocking your tank outflow... When you are taking showers more water flow in to the tank and it fills the tank to the top which makes water on the ground... Its better to call your service, they will fix it..