Translation:I have read all the books on the shelf.
“I have read” is called the present perfect tense, but it is actually a past tense that either continues to the present, has recently happened or it affects the present. “I read” is the simple past which has no limits, so we don’t know when it happened and it overlaps all other past tenses, so it can also be used instead of the present perfect, but it gives less information about when. You can refer to the timeline to see which tense is better for a particular time. https://www.thoughtco.com/english-tenses-timeline-reference-4084637
"I read all the books....." - 'read' here the past tense of the verb 'to read' - was not accepted. DL says 'I have read all.... ' is the correct answer. I disagree. If I read (past tense) all the books in the past, it's done. and past tense should be used. If i started reading all the books on the shelf some time in the past (yesterday or years ago, whatever) and am still reading all (!) the books then "I have read all ...." is correct.
Programmers may not have figured out how to tell the difference between the written forms of the present tense “read” pronounced [reed] and the past tense “read” pronounced [red]. Try reporting it as also correct, but “have read” can also be used for the recent past which is also finished and for a past that affects the present. If you are still reading, you would use “have been reading” instead. If you have just finished reading or finished today or even yesterday, then you could use “have read”. If you are talking to the teacher who wonders if you are ready for class, then you could say “I have read the book.” even if it was a long time ago, because it affects the present.