The floor of the bathroom is not very flat, and there is standing water after every shower, and then

It is impossible for the bathroom to be completely free of stagnant water, is the perimeter of your toilet completely sealed? If not, then there will be water seeping in, and as long as there is standing water, mosquitoes will lay eggs inside. The impact doesn't have any effect, it's just unhygienic.

Where there is stagnant water and smell, it is difficult to avoid breeding all kinds of mosquitoes, gutter moths and other insects to lay eggs and reproduce, you can often scald with boiling water, or spray insecticides to kill insect eggs, so as not to breed!