Wet room floor leaking onto landing

1. Walk in showers and wet rooms can be WET spaces that are completely open or semi-wet. Most people will go for a semi-wet design that allows for a dry space within the bathroom. Instead a tiled floor that’s graduated toward a central drain in the room, separate the actual shower area and place a drain under the overhead rainfall showerhead or power shower head, so that the water remains contained under the shower itself. Even if you don’t use doors, the floor can have a lip to keep water inside a specific area (best if angled in a corner). It’s also important to situate your power shower head so the main spray falls down or across where splashing isn’t an issue. Consider placing the showerhead on a pillar instead of a wall. But always, install the head or manual device or console showerhead to face the back wall or to the side, not out into the room. 2. Whether you have a large console power shower head that has dozens of settings and a massager, or a soft rainfall panel inset into the ceiling, the angle of the floor is extremely import. To avoid pools or water collecting where they aught not, the drainage must be engineered to slope gradually below the shower. A bathroom can have an open doorlesss area yet have space that never gets wet (not more than what damp bare feet track around) if all three of these elements are finished with care: (a) choose the showerhead placement wisely; (b) slope the floor toward a single drain under the shower; (c) consider adding a small lip around one area to contain pooling.

From your description . If you have water rolling out door way . you can get rubber door bar/threshold . easy fit .fix with a mastic to stop water. Can be fitted over the top of existing floor . Which can stop the water from getting out of wetroom area. If it's a mist from your shower . A screen would sort. Or fast fix shower curtain with adjustable or even removable pole .

Check the filter is not blocked and preventing the correct drainage for the water.

Is the waste partially blocked causing the water level to rise over the threshold ? Is the gradient of the showering area too shallow or too small ?

Wet rooms are tricky, need to have proper falling towards drainage and need to be checked regularly for hair, the common problem of blockage, if those aren't the issue then either put a threshold to stop the water in landing area or Glas screen