After starting Local in administrator mode, the problem was solved.
I use a user with administrator privileges and when I use Local I do it by booting in “standard” mode.
So, considering that I was unable to change the attributes of the wp-all-import folder, I have to conclude that the problem that was preventing the file from loading was Local’s startup mode. Question: does Local’s specification require or recommend starting with administrative privileges?
Regarding the username syntax, are there no important reasons why I should not continue this way? This question is motivated by my inexperience as a windows administrator and my lack of confidence in this OS. I have enough headaches procured by the complexity of web project development work, going to wake sleeping dogs…
Many thanks for your help.