Hi Toufiq,
I re-enabled the extensions you mentioned earlier and the error did not repeat. I cleaned the site cache again (I do it every time, I directly delete the files on the server and those of the browser) but the error did not reappear. I'm starting to believe in ghosts ... (just kidding). I also went to the site you gave me but I did not understand anything, there is not my site below, loaded, and then it is Joomla 4 that I have not yet experienced, because the Indigo template, for what I have seen on yours site, it is not compatible with J4 but only with J3: can you confirm this for me?
Anyway, thanks always for the help, the courtesy and the patience in following me: I am not young and not very practical, I try to do the best I can, really wasting a lot of time, but I can't do anything else. Thank you!