No one could show a small demonstration sketch that I asked for here: https://forum.arduino.cc/t/resolved-without-hacks-how-i-used-f-flash-memory-strings-in-snprintf-etc-for-arduino-nano/891927/14
And I could not make it work myself.
So if no one can give some prove, then Whandall is right and the others are wrong and it is wrong information or fake or bad documentation.
The Arduino MKR Wifi 1010 does not need PROGMEM. I think it is enough if you make a string a 'const'.