The answer to 'why is my shower overflowing' is that the drain is likely clogged or blocked, causing the water to back up and overflow. This can happen for a few common reasons, such as hair, soap scum, or other debris building up in the drain over time. As more water tries to flow down the drain, it has nowhere to go and starts coming back up through the shower floor.
If the shower is overflowing, the first step is to try to clear the clog yourself using a plunger or a drain snake tool. However, if the clog is deep in the pipes or the problem persists, it's best to call a professional plumber to diagnose and fix the issue properly. Attempting to disassemble or work on the plumbing yourself can often make the problem worse if you don't have the right skills and equipment.