I have now searched all the settings in the control panel and the phone app, but I could not find any function for automatic call acceptance. I have to say, however, that I have the Fairphone Open Source OS on it, not the standard Android. It is possible that there are differences here.
I can also imagine that this could be installed later by means of an app, perhaps with root rights, which you can simply switch on and off with the Fairphone, at least with the open source variant of the OS.