The clapping's fine if it's an opportunity for people to get together and think about what the NHS staff do, and appreciate what the NHS is there for, and why it's so important to keep the NHS, and to keep it strong.
If it's an excuse for people to feel good about themselves for five minutes despite having consistently voted for politicians with a strategy of underfunding public services so they aren't fit for purpose so that the best bits can be sold off to their mates because "the private sector can always do it better", then it's nothing more than a gesture.
There are people who took part in the clapping for the former reasons and people who took part in it for the latter. There's nothing wrong with the action in itself as long as the question is "what next?" and how to follow up on it.