Is there a pole device to sand a wooden deck manually?

same tool will do.  just replace the drywall screen with sandpaper.  better yet, use a power sander on the deck

Repurpose a drywall sander and you are good to go.  

But like Bob Dylan, I would do the Judas bit and go electric on this.

No. Usually you use a belt sander with lots of 36 or 24 (or lower) grit sanding belts. and you get down on your knees and do it. Maybe move up as high as 60 grit.? Really depends on how the sand paper gets clogged.  You have to look and check the paper.  If it is clogged up, it don't sand no mo.  You chuck sheet for new one. and continue. You can rent a drum sander and the necessary sandpaper you buy because once clogged they are garbage.  Those people who redo hardwood floor coatings because over the many years the varnish gets darker or yellower so the entire floor gets it(halls, auditoriums, gyms, bowling alleys.  It is a costly process and fair long time of work so at least 25 years goes by before that happens.

There is a walk behind drum sander available at rentals and probably HD.

Make sure all nail pops are hammered down and/or screws are not protruding above the wood.

Yes. See example. https://www.hirehere.ie/sander-squarbuff-finishing

Just use a drywall sander.

It is exactly what you're talking about.

Just point it down rather than up.

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@Barry - The question was specifically about manual sanding.  Not powered.

@T C - Same point.