Not sure what to do. As long as I can get back my old data files, should be fine. Right now I use new testing user. I need step by step A-Z ( simple language starting what to download etc.) for the answers regarding to the USB live system (seems the only way perhaps). You can see the details in the link about my questions, comments and answers by people. Here is the link https://askubuntu.com/questions/1045401/cannot-sign-in-my-laptop-after-sudo-admin-problem-in-terminal.
Your AskUbuntu thread is the correct place to seek technical support, and looks like there’s a good answer there already.