Newer versions of Skyline are always able to open files from older versions of Skyline.

That error message is saying that you are running Skyline version 21.2 and it is unable to open a file which was created by Skyline 23.1.
That is, an older version of Skyline is unable to open to a newer file.

It sounds like you wanted to be running a newer version of Skyline but the actual version you ended up running is much older.
You might want to go into "Programs and Features" in Control Panel and uninstall all of the unwanted Skyline versions that you see there.

By the way, if you are running a newer version of Skyline and need to produce a file which can be read by an older version of Skyline you can use the "File > Share" menu item which will allow you to specify an older format to save as.
-- Nick