One further thing to bear in mind here is that some causes of death can be expected to be decreased on account of lockdowns e.g. accidents - less people out and about, less people driving etc. will naturally lead to less accidents. Of course on the flip side, more people stuck at home & using the time to do renovation work etc. could lead to an increase in e.g. power tool related accidents.

Other causes of death such as flu can likely also be assumed to be decreased as a side-effect of lockdown

Contrariwise, people are avoiding treatment for other illnesses for fear of catching COVID in a hospital. Many people are depressed or even suicidal. And people are less active, which aggravates other health problems. All of these factors could increase the number of deaths.

3 months of lower activity is not killing people in those 3 months.

Any effects will be felt on a much longer timeframe.

Most office workers have very sedentary lives anyways, that didn’t become significantly more sedentary when they replaced their drive with a walk to another room and working in an office with working in that room.

Throw in the fact that they are likely cooking more because restaurants and all were shut and not just having lunch delivered to their office, they may even be getting more activity in.

Plus no commute leaves more free time in the evenings for exercise etc. Obviously not everyone will be doing that, but anecdotally a few people I've talked to from work are going for more walks & cycles etc.

If it was significant in comparison, we would not see a sharp drop in deaths after the lockdowns.

Do people get depressed and die because of a lovkdown? Sure, I got depressed as well. But the numbers show that this issue is far less than the number of people that would die otherwise.