Is it glue down or floating/click together? The shower goes in first. Then the flooring IF it is "permanent" (like glue down). If not, then it must float. And toilets have problems with allowing flooring to "float".

So this all comes down to the TYPE of install. Which is it? Glue down or floating?

I worry that the toilet will act as an "anchor" if you run the floor underneath the fixture. A glue down vinyl plank would be a better option....I've seen this done both ways. The floating floor run underneath the toilet as well as the floating floor run UP TO the toilet.

The thickness of the vinyl will dictate how well it will work running UNDERNEATH. A thin (4mm) vinyl has a VERY small click-profile. The size of the click-profile tells us the STRENGTH of the click edge. The smaller the profile the LESS strength it has to stay together.

A thick click-profile (8mm- 12mm) can accept a little bit of stress without coming apart. How thick is the vinyl plank you are planning on using? Name? Brand?

That isn’t a suitable choice for a bathroom. “Waterproof” only means that it isn’t damaged by water. It still allows water to get underneath and your subfloor to be damaged. You need sheet vinyl if you want vinyl in a bathroom. Not pieced vinyl.

with kerdi membrane you could use vinyl tile the membrane would be totally waterproof to protect your subfloor

Concrete is porous. It will wick water a long way. Far enough that it can damage the framing sole plate and encourage insect infestations.

Should the concrete be sealed?