When a shower starts to drain slowly, when you find yourself up to your ankles in water it may be time to perform an intervention on the clogged drain.
Plunger
Flood with warm/hot water and plunge hard for several iterations
Remove visible debris
And pull out hair tangles near the top.
Pour baking soda & boiling water
You may need to repeat this process a few times.
You can start with boiling water to loosen the gunk.
Use generous amounts of baking soda and boiling water to quickly unclog it.