Low thresholds are accessible, not to mention safe for everyone. Flush is ideal for all interior thresholds, but aim for 0.5” if some height is necessary for doorways leading outside (to keep water out).
If you can’t roll a small ball (e.g., a golf ball) over the threshold without a lot of effort, then it’s likely too tall. Just like the ball might stop with a threshold in the way, so will smaller wheels on the front of walkers and wheelchairs. If this happens to someone using a wheelchair, their chair will stop, but momentum will keep their body moving forward, leading to the unwanted potential of launching onto the ground. The same thing applies for people walking through a doorway who might have difficulty picking their feet up.