Anmeldung requires a residential address the local registration office will accept. That does not always mean you must sign a twelve-month lease in your first week—though some cities and landlords make temporary paths harder than others.
Landlord confirmation letters
Many municipalities ask for a Wohnungsgeberbestätigung. Temporary flats, employer-arranged apartments, and certain serviced residences can provide this if arranged in advance. Ask before you pay a deposit.
Sublets and shared flats
Shared flats can work when the main tenant or landlord cooperates. They fail when nobody will sign the confirmation. Treat that signature as a gating item in your relocation plan, equal to the apartment itself.
Why rush leases go wrong
Candidates sometimes accept a poor lease simply to register. A calmer path is a short temporary stay that explicitly supports registration, then a longer search once you hold your Meldebescheinigung and can view flats in person.