All my set ups, most all I transferred over and new files disappeared!

I have a 2021 MacBook Pro, version 12.5 (Monterey). I am not very techie but I was able to transfer a good portion of the data from my old computer to it. I started learning the new computer, using Safari and other apps on it including creating documents.

About a month or so later, while I was using Safari, a window asking for the 'keychain password' suddenly popped up. I thought it was a little suspicious so I tried to cancel it but the window just wouldn't go away after many tries.

Then I tried to close 'Safari' and I couldn't do that either. Safari was either locked up or that small window was stopping me from quitting the browser. So I did a 'forced quit' and then I shut down the computer and rebooted just to be safe... seems that was a big mistake!

When the computer booted back up, all files and most of the apps on it were gone! It was as if it was a new computer with nothing on it but the basics that it came with. Most all my set ups, most of what I transferred over, all new files, etc... were gone! :(

I am afraid to use the new computer now just in case I might overwrite the important documents I had on it. So I am stuck using my very old computer for now until I can troubleshoot what is going on and hopefully retrieve everything that was on it. I need to figure this out soon because the old computer is starting to get very glitchy.

I did check in 'About this Computer' and the storage information shows there is 103.58 GB in 'Other Users.' I am wondering if that is indicating the files, etc that are missing? To be honest, I have no clue what 'Other Users' means. Are my files, apps, etc gone and have to start over? Or are they just hidden?

I really hope someone can help me. Thank you in advance.