To move/update your wallet.dat file from an old desktop to a new computer,
-snip-6. Replace the wallet.dat file in the Bitcoin data directory with the one you copied from your old desktop.
That is mainly used in the very old version when Bitcoin Core didn't have multi-wallet support.
Something our friendly neighborhood AI chat bot would answer.Now, it's not recommended because Bitcoin Core now has a native way of importing wallet.dat files like the one in my instructions above.
Additionally, it's not good to replace files while Bitcoin Core is running as it may introduce inconsistencies or even file corruption in some cases.