What are the ways scholars use to remember loads of information from the chain of narrators to a hadith, to the risele Ameliyye, to everything else?

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It is mainly light placed in their hearts from Allah (swt). To have strong memory is possible and a number of recommendations exist.

Please check this link

https://www.al-islam.org/pursuing-excellence-guide-memorising-holy-quran-sl-al-hakim/part-2-how-memorise-holy-quran