Try using Disk Utility in Recovery Mode (you described doing that in a post in another thread) to change your password from blank to something with characters. I seem to recall that more recent versions of OS X do not like no characters as a password.
On a Mac since 1984.
Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
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