After a bit of tinkering I managed to fix my speed dial page. But after restarting my PC and Opera, I find the speed dial page empty again. I thus exported the speed dial bookmarks to html from another PC with Opera, and I copied this file to my PC to import it.
This is the result :
Snap-01_20240501_Speed_dial.jpg
SM-a528B is my smartphone bookmark;
Desktop-5MPD2F5 is the bookmark from my first attempt, emptied by hand;
Desktop-5MPD2F5 is the bookmark of my second attempt, made with your help and now empty, because I had moved all the links to the Accesso Rapido root (speed dial);
Desktop-U0BRSGH is the bookmarks imported from the second PC.
I could move the links again by hand as I did yesterday but since I find, from all the tests done, a series of old bookmarks imported by mistake in the previous days, I think I will uninstall Opera and all the data, to try to import again that HTML file from second PC