Great !
The first phase (the replacement of the 2 files with the ones from WinXP) worked greatly.
But in this way I lost the bookmarks already accumulated in Win10 (however I preserved those replaced files).
Using the Opera browser function "export bookmarks" created an .html file of the bookmarks in Win10, .html file that
enabled me to import/recover the Win10 bookmarks.
Many thanks again.

Help !
I need to import bookmarks from opera browser on windows xp 32bit to opera browser on windows 10 64bit.
I tried suggested methods but I did not succeed. I found various opera bookmark files in winXP, I tried to copy them in win10, no one of those files have extension, I tried to give them the extension .html to import them, but without success.
Many thanks

Is it even possible to preserve/merge with the new bookmarks already accumulated in Opera browser on Windows 10 ?

Great !
The first phase (the replacement of the 2 files with the ones from WinXP) worked greatly.
But in this way I lost the bookmarks already accumulated in Win10 (however I preserved those replaced files).
Using the Opera browser function "export bookmarks" created an .html file of the bookmarks in Win10, .html file that
enabled me to import/recover the Win10 bookmarks.
Many thanks again.

Is it even possible to preserve/merge with the new bookmarks already accumulated in Opera browser on Windows 10 ?

Help !
I need to import bookmarks from opera browser on windows xp 32bit to opera browser on windows 10 64bit.
I tried suggested methods but I did not succeed. I found various opera bookmark files in winXP, I tried to copy them in win10, no one of those files have extension, I tried to give them the extension .html to import them, but without success.
Many thanks