Would you still have given him this same choice if he was a key worker or lived with one? Or what if had given you the choice of boot any live-in partner who was a key worker or don't see the children?
However, based on what you have posted you make no sense tbh. You don't want him to be physically in contact with the children so is seeing them through the window. Yet even though he is keeping his distance, obviously he cannot communicate as he would normally do, he is still doing so. But somehow he is in the wrong.
The gardening is ridiculous none essential work that over the past however long you could have been tackling this. But instead, you chose to prioritise certain aspects of a home and the garden has become to the point of its current state. It's irrelevant what he did prior to the separation, now he will realise the place needs doing up as potentially it might need to be sold. Not everyone walks away with the family home after all.
Who knows maybe your ideas were ridiculous and most people would burst out laughing. Instead of you deciding to walk away and stop engaging, you decided instead to close the blind which effectively ended contact. How did that benefit the children? They should not be brought into these squabbles.
You have shown them that it is you that is stopping them from talking to him. Whatever issues you have you really need to find ways to deal with them without including the children. They will remember this and if either of you tries the blame game in future about this, you will come across as the bad guy either way.
Its all well and good saying visitation should be suspended. Erm, what about the detrimental impact on children? What about their legal right to see their parents? As adults, we should be able to cope even when a relationship ends. Children don't have these tools needed to deal with this. Their worlds have already been turned upside down from the separation, on top of that the usual family stuff that can happen, on top of that CV19, and now one of the few things that maintain a small resemblance of normality for those children, they are now supposed to not see their parent even from the outside looking in assuming, of course, there are no injunctions in place already to prevent the person from going to the home. They aren't allowed to talk to the other parent even by observing the distancing rules in place, why not?