Not sure if this has to do with your product or VS2022 itself, but it points to PHP specifically.
Normally, when you make changes in a file, the changed lines are indicated on the left side of the window with a yellow line. When you save the document, the line turns green.
Since the last update, any changes saved that are PHP specific, the color changes from yellow to a dark yellow. Hovering the line show the tool tip "Change - Not saved". The file was successfully saved, and if you close it and reopen it, the changes are there.
The reason I say it points to PHP Tools is that this only occurs for PHP code. When a document with HTML and PHP intermixed is worked on, any changes to the HTML show the green "Saved Changes" bar on the left, while any changes to any line with PHP code in it turn dark yellow.