How imperceptible will the 4-July-2020 penumbral lunar eclipse be?
Completely imperceptible except to instruments.
Space.com reports

In general, most people don't notice the penumbral shadow projected on the moon until at least 70% of its diameter is covered. Some people who have very acute vision and better-than-average perception might notice an ever-so-slight shading when only 50% of the moon is inside the penumbra.

As your image shows, this is a lot less than 50%. Nothing will be observed by the naked eye.  &quot;Visible&quot; in your first source only means &quot;the moon will be above the horizon at this time&quot;. It doesn't mean you will be able to see a change or dimming of the moon.