I am attaching a photo of what I have done.
This hole is not suited there, but how much it is going to affect the performance of the antenna?
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If the hole is empty and is not metalized, then it won't affect the performance of your antenna.
If the hole is meant for mechanical fixing, use plastic screws.
Metal screws might de-tune your antenna.
A small metal screw won't affect much the overall performance of your RF system.
What de-tunes antennas are walls or big objects.
If your product is wall mounted than the wall will certanly de-tune your antenna a certain amount.
Heat staking the PCB to the chassis or plastic screws for sure. The steel will induce (attract) the magnetic field to some degree. Even "non-magnetic" stainless steel alloys can be somewhat magnetic depending on how the screw was formed because work-hardening and/or thread-cutting can change the magnetic properties on alloys like 316SS.