Major issues with Pages 15.4

This needs more explanation if you expect a solution. "Locks everything" needs more specific explanation about the steps taken prior to that cause. If the administrator is not the original creator of that password-protected Pages document, then no admininistrator privileges will unlock it. Not Apple. Only the original document creator.

I am using Pages v15.4 presently on macOS 27.0.1 and am the sole user and adminstrator. I have no issues with Pages v15.4.

I am able to open Pages documents created by Pages '09 v4.3 and all intervening versions of pages through Pages v15.4 — without any compatibility issue.

Describe what Pages 15.4 does, including any dialogs, that may occur leading to your term incompatible?

What version of Pages were you using on macOS Sequoia? Did any of your documents that you moved over to 27.0.1 depend on any custom user templates that you created there? If those My Templates were not copied over to Pages v15.4 My Templates location, any documents dependent upon those inherent custom templates will cause Pages to revolt.

Sequoia 15.7.4. Pages 14.5 and no custom Templates. Tried to open a pages file "Charity" This is what I get...

"Charity.pages" can't be opened right now. Pages couldn’t read the file. You can try restoring to a previous version. Browse All Versions.

P.S. It won't even open a jpeg file.

Pages will not directly open image files. For that, use Apple's Preview.

You can drag and drop supported image files into a Pages document, or via the Insert menu > Choose File menu item, or even the Toolbar Media menu.

If Charity.pages is an empty document, Pages will not open it. If it was a file format that Pages does not open, renaming it to a file with a .pages extension won't help either. If it is a damaged Pages document, restore it from a Time Machine backup.

I am on 15.4 Pages and 27.01. All my Pages files that I moved over from a Sequoia MAC are incompatible.

Jpeg files won't open "may be damaged"