переустановка mac os

If the instructions in the Apple article @Grant provided does not allow you to erase the system, then you may need to perform a DFU Firmware Restore if it is a 2018+ model with T2 security chip (2018-2020) or M-series Mac (2020+). However, this process requires access to another host Mac that is currently running macOS 26.x Tahoe (or possibly macOS 15.x Sequoia).

If the locked Mac is an M-series Mac, this will erase everything on the internal SSD & push a clean copy of macOS onto the internal SSD. If it is an Intel T2 Mac, then this will destroy all data on the internal SSD, but you will need to reinstall macOS using Internet Recovery Mode.

How to revive or restore Mac firmware - Apple Support

Edit: Whenever you acquire a used/preowned Mac, then you should follow the steps in the Apple article @Grant linked (at least starting at the steps from erasing the Mac) so you can possibly identify some of these potential issues while you may still be able to contest the sale with the previous owner & get your money back. Some issues cannot be resolved by the new owner if a previous owner has FindMy enabled on it, or the Mac is still being controlled by an organization's MDM management system.

the proper way to proceed is this:

First, try to be sure you have a backup copy of your files.

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

auto-translate:

Reinstall Mac OS

When reinstalling mac os, it requires the credentials of the previous owner when activated, although the macbook is tied to my apple id

--------

MacOS is not copy-protected in the usual sense:

Apple software downloaded from the Mac App Store, including MacOS, is not copy protected. However, it IS tagged with the Apple-ID of the purchaser when "purchased" (or equivalent. Think of MacOS as purchased on sale for $0.) A valid Apple-ID is required for almost all downloads from the Mac App Store.

You cannot update, upgrade, or install new software based on already-installed software UNLESS you supply the Apple-ID of the original software.

see additional information below