It always amazes me that some tile contractors don't know that water runs downhill.

Something similar happened to me. The depression in the shower floor was possibly from where the tile guy was kneeling.
My contractor fixed it on his dime.
He laid a new tile floor over the old one so that the waterproofing wasn’t adversely affected. I’m quite picky about aesthetics and it has always looked good to me- I really can’t tell a difference. It’s been almost four years; no further issues. This bathroom shower was in a basement- I don’t know if that made a difference.

Put a straight edge on the floor- ruler, level, etc. The whole floor should be flat and sloped toward the drain.

They call that a bird bath, up to you if it gets fixed as the fix is a complete redo of the pan including tiles up the wall (at the very least the first few courses) as the issues is in the pan before the tile was laid.

A squeegee is cheap and easy, and should already be in use after showering. Because, the only real way to fix that is expensive and complicated.

Update: we ran the shower for 15 mins and if someone stands in the pool the water flows outside of the shower because the pool is fairly close to the edge.

Then you have a full redo on hand. It also sounds like a full redo of the room floor as well, since the shower is getting water into the room. It's likely technically too small to be a curbless shower without sloping and waterproofing the whole room, to create a wetroom. This is more than a "redo". It's a full redesign and redo. WIth possible structural changes, since the curbless wasn't done correctly the first time.

OP - will you provide a photo of the shower from farther back? Try to show the entire shower if possible.

Also, if you have any photos that you took while it was being consructed, post those also. I took quite a few while mine was constructed - it's always good to have them if needed later (also, my SO was always asking me to send updates).

This is your contractor's issue to remediate - he/she is responsible for constructing the shower pan without any bird baths (and should have checked for those prior to installing the tile).

Do not let the contractor try to talk you into a quick fix. While having new tile installed over the existing tile may have worked for chinacatpeekin above - if your pan is retaining water and you add another layer of tile over, the water will still be there (regardless of whether you see it or not) = stagnant/moldy/disgusting - especially with the amount of water your pan is retaining after a 15 minute shower!

If water is getting outside your shower, then your curbless has an incorrect slope. If it has an incorrect slope, then likely a whole lot else is not done correctly. Like waterproofing. More pictures would help with a definitive diagnosis. But the initial diagnosis is terminal, with full gut and redo.

Had a similar issue where water sat at one end, drain in the middle. A small squeegee (like you use to wipe water down the walls/glass) to move water to drain. My shower is dry in 20 minutes.