This is the problem with blind followers that they even question the word of Allah.
Even though the verses are clear that the Quran is complete and detailed, you still dare to question Allah.
Here is another verse for you that Allah is not short of words.
31:27 If all the trees on earth were pens and the ocean ˹were ink˺, refilled by seven other oceans, the Words of Allah would not be exhausted. Surely Allah is Almighty, All-Wise.
Since either you are really dumb to understand or does not want to understand, let me put it one more time in simple words.
First, a funny story for you to explain you what you are doing. A man went to a shop to buy some groceries. He asked the shopkeeper how much for the 1Kg tomatoes. The shop keeper said Rs. 100 for 1Kg onion. The man asked again how much for 1Kg tomatoes. The shopkeeper replied Rs.200 for 1 dozen eggs. The man asked again how much for 1Kg tomatoes. The shopkeeper replied Rs. 300 for 1Kg apples.
The simple question I have asked is that if Quran claims as above that Quran is complete and detailed then please give me reference to detailed steps to pray salah from Quran?
If there is none then either Quran is wrong or your understanding of the context of this claim is wrong that you are putting this claim in a wrong context. So go ponder yourself about the above Ayah and don't quote random references from Quran just googling in 10 min without understanding the context of those ayahs. Otherwise if you apply this claim that Quran explains everything literally then there are many things that Quran don't explain. Then wouldn't the Quran claim would prove wrong? So, use your brain a little bit and next time before giving any more reference please first give me the reference in Quran with detailed steps on how to pray salah. And if there is none then you need to understand there are two sources of our deen. Quran and Sunnah of the Prophet PBUH (which now exist in the form of Hadith). Now, if there is a contradiction among some hadith and Quran then we go with Quran. Otherwise, we understand our deen from both Quran and Hadith in a manner where Quran provide the guidance and set the rules and then there are hadiths which explain those and you cannot just discard all the hadiths. There is a science of hadith classification that scholars have derived over the last 1400 years and then when we apply a hadith we make sure that it is not in opposition to Quran.
And regarding your sentence:
Anti-Quranist cults are waiting for someone to save this world, in other words, they are saying that the Prophet Mohammad was not the last Messanger of Allah.
Who is saying that if Imam Mehdi will come he will proclaim prophethood? This clearly shows your low intelligence level to derive this result from the quoted hadith that Imam Mehdi will proclaim prophethood. The deen is complete and there is no new thing that is going to come.
Now, for your education, if you are really interested to understand the Quran, the claim of Quran that it is complete and detailed is "in the context of explaining the reality of the world (which includes who created this world, why this world was created, how this world will be destroyed i.e. judgement day and what is going to happen after that day)". It is low IQ people like you who thinks that Quran is claiming that it explains every phenomena, every event and every science equation in the world because if you accept this claim then you are opening the door for someone to prove Quran wrong. Every reference that you have mentioned above is about Quran asking people to not blindly follow Quran but question it and ponder on its ayats but it never says that Quran explains every little thing in this universe. E.g. you mentioned this Ayah:
[Quran 6:38] We did not leave anything out of this book.
If you read this ayah only, it seems Allah is claiming he has left nothing out of this book (although there are issues in this translation) but then you are quoting this ayah out of context. If you go and read all the ayahs before and after it and try to connect them in a homogeneous way, and
ponder a bit (i.e. use your brain) you will come to the conclusion that the translation that you mentioned of "this book" is wrong. Here Allah is talking about "the book" of decrees (the preserved tablet) that everything is recorded in "that book". Otherwise putting Quran here will result in proving Quran wrong.
I hope you will ponder a bit on my reply instead of making it on your ego to just try to put me down.