There is a list of top richest bitcoin wallets at this moment.
How can I find the list of top richest wallets on other dates in the past?
You can use blockchair.com. It allows to easily search and analyse the Bitcoin blockchain (also Bitcoin Cash and Ethereum).
In your case, you can sort the transaction outputs (addresses) descending by value and optionally specify the time in the time field so you get the top richest addresses at that time.
I did some research and I think the only way to achieve this is through having database of all-time bitcoin transactions associated with their wallet addresses.
Having database, you can filter out the addresses existing at given time in the past and calculate the balance of each address summing up all unspent transactions of it at that time.