Well this is disappointing to put it mildly. It should work, it doesn’t work, and WordPress offers no technical support. Only this board that doesn’t have the answer.
I guess it’s time to explore WordPress alternatives. The alternatives may not have tech support either, but at least their basic services won’t arbitrarily stop working (in theory).
The only things that have modified my website between the time when it worked and the time when it didn’t are updates. So WordPress broke it and they offer no help to fix it. Disappointing to put it so very mildly, cleanly, and calmly.