Tbh I don't have that much of a problem with this...hear me out.

Your point is exactly correct, this law would not be able to be enforced unless you did genital inspections. That means that trans people will be able to freely use the toilets of their choice because clearly they're not going to inspect everyone that goes in.

The law would only be able to be enforced in the case of foul play. So say a cis man went into the womens toilets to sexually assualt women or creep on women. There may be insufficient evidence of what they had done (since many toilets don't have CCTV inside) but you can guarantee there would be CCTV of them going into the womens toilets. So this makes men who might do this more likely to be prosecuted at least for using the wrong toilets.