Can I use wood putty on my deck and then paint?

Since a deck receives so much exposure to the elements I don't think you will be happy with the results of putty for repair. I would go ahead and replace it. If it's pressure treated lumber, you will need to wait at least 3 months before priming and painting.

If it is a problem with only one board, I would replace that board. But only, because I think once you start painting a deck, you are going to have to maintain that all the time. If your deck is hit with really hot sun (or a lot of rain), you may have to repaint every year or two.

Yes, replace the worn out board if compromised and the structure of support is ok.

Replace the board. Wood putty would just pop out with expansion and contraction.

Thank you for helping me . I did not know what to do?