The way I have done it in the past, is to open Task Manager, click on the Services tab, then right click on one, and select Open Services. You will get a list of all services running . Find the 3CX ones, right click on each, select Properties, then set the Startup type to Disabled, or Manual.
You may have to stop each service first, and there may be a specific order, as some may not stop until you stop one of the others.
There may be another way, but this is what I've done in the rare occasion that I don't want 3CX staring on a particular machine, but don't wish to remove it.