This might sound rude but why should you clap for someone doing their job . That they are paid to do

In the case of the NHS, they are going above and beyond what they are paid to do and above and beyond the value of their pay. They are taking on a lot of risk, more so than usual, with inaqedate protection in many instances. While most of the country retreated into its shell, they stood on the front line like soldiers do. If your job suddenly got 500% busier you'd expect an increase in pay at the very least. If suddenly you had to handle corrosive subtances as part of your job you might expect PPE and maybe some danger money. When none of those things are on offer a round of applause seems the least that people could do for you.