An always recurring question is how ESD safety can be achieved while maintaining isolation.
One thing is that it is quite impossible for a single device for both maintaining 4 or 5 kV isolation and having a path for ESD strikes through the isolated worlds. There are solutions for this, though. One solution is a combined EMI/ESD coupling capacitance that would be placed either at the isolation point or somewhere near to the human interface.
Another solution is risk management. You only need ESD protection at the particular points that can be touched by the user. And this is usually written in the product risk management policies, which are defined by you as manufacturer.
Here is a good article that helps to understand ESD in isolated environment:
Intona 7054-X(M), 7055-B, 7055-D
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