Admin password not accepted for updating system software

I was finally lucky. By following the suggestion mentioned in another post in this forum, System Preferences won't accept password … - Apple Community, I managed to solve this issue. Basically, I had to enter into Recovery Mode and execute the command 'resetpassword' inside a Terminal. I modified the password as if I had lost it (well, I had to enter my password previously for arriving to that step, what makes that assumption a bit confusing), and with that my problem was solved.

I leave this message here just in case that I might help someone with this problem.

I am afraid I did not explain that I performed already that procedure that you suggest. Anyway, what it currently worries me is that the admin password is not accepted in the step described. It behaves exactly as if I would type in anything else. Moreover, in that step another window is also opened asking for rebooting the system in order to rebuild the extensions database, and I have also done that, but it does not change anything after reboot.

I had the system installed for some years, performing updates even on the Mac operating system, as usual. Some day last month I touched something that made that I could not start the system anymore after logging in. Therefore I had to start the system in recovery mode for reinstalling the operating system, as if it were from scratch, but the disk was not formatted. I could access finally to the previous data I had in my account (that was tricky as well -- it appeared as "inaccessible space" in the disk, but I managed finally to access to it.

I was wondering since the beginning whether this could be the reason that now I would not recognise the "new" password when trying to make this operation. I am using in principle exactly the same one, yes, but who knows whether it were stored differently because of a cryptical issue and now it could not be recognised when put in -- don't know, I am just trying to guess. Because all of this I had finally placed my question here for some help if possible.

Thank you very much for your help.

Right now there are two, but I only used the second one for making tests, to see whether I could solve something.

Concerning what you have added, I was also trying to find a procedure for setting "me" as the "true owner". I will explain...

After the recovery, in the initial steps when installing MacOS once again, I had to place "me" with a local account on the computer -- I had problems for connecting to iCloud. Later, after being able to progress in the MacOS installation with that "initial" account, I managed to connect to iCloud but... I found strange (in my innocence) that I could not update an application from the Apple Store because I was not the owner of the computer. That was an issue I did not understand, and that is why I was trying to also look for a way to state myself that it was *me* the owner of the computer. Later on I found a way for updating the application from a terminal, but I had the impression that I had missing something left to be fixed: the true ownership of the computer.

Right now I have the Apple Store connected with my iCloud identifier, I may install new applications, but I do not currently know what it might happen if I would need to update one of them -- at least from the Apple Store application.

Perhaps that is the true problem that make things not working as expected. How might I check and solve that issue?

That is the last option I would made if possible. I would prefer some way of checking who is the "true owner" for the system and how to change it if it were not me. Moreover, it is supposed what I did -- reinstall the MacOS, so I have the doubt of what might be different...

The result is True.