Hi @bouchacha, welcome to the forum!
Sorry to hear you’re having issues with the restore performance. Duplicati can restore individual files in a timely manner, but it relies on certain things to be able to do so otherwise it falls back to slower methods.
What version of Duplicati are you using on what OS?
What is your dblock (Upload volume) size set at?
Are your restoring through the job (which should use they job database) or direct from the backup (which builds a temporary database)?