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Muslims are encouraged to say “I don’t know” or rather “Allah knows best”.

There is famous story of a man who traveled to visit the respected scholar of Islam Imam Malik ibn Anas (may Allah have mercy on him). The man presented him with 36 questions to which Imam Malik answered only four.

Surprised, the man said:

“I have come from such a faraway land, and people told me that you are the most knowledgeable scholar. What should I tell them when I return?”

Imam Malik replied:

“Tell them that Malik does not know.”

About the young men in Surah Al-Kahf, Allah Most High says:

قُل رَّبِّىٓ أَعْلَمُ بِعِدَّتِهِم مَّا يَعْلَمُهُمْ إِلَّا قَلِيلٌۭ ۗ فَلَا تُمَارِ فِيهِمْ إِلَّا مِرَآءًۭ ظَـٰهِرًۭا وَلَا تَسْتَفْتِ فِيهِم مِّنْهُمْ أَحَدًۭا

Say [Prophet], ‘My Lord knows best how many they were.’ Only a few have real knowledge about them, so do not argue, but stick to what is clear, and do not ask any of these people about them [18:22]

And:

قُلِ ٱللَّهُ أَعْلَمُ بِمَا لَبِثُوا۟ ۖ

Say [Prophet], God knows best how long they stayed.’ [18:26]

Peace & blessings upon the Nabi of Allah.