The document cannot be saved as jpeg without losing information

You’re getting that dialog because your file contains a saved selection in the Channels panel. JPEG format doesn’t support saving extra channels like alpha channels or saved selections — that’s why Photoshop warns you about losing information.

To fix it:

Delete the saved selection from the Channels panel before saving as JPEG:

• Go to the Channels panel.

• Look for any extra channel named something like Alpha 1 or your saved selection name.

• Right-click it and choose Delete Channel.

• Now try saving as JPEG — the dialog should no longer appear.

This wasn’t shown in older versions because Adobe added stricter file compatibility checks in recent Photoshop updates.

I noted that it only happens if there are multiple layers. Make sure to flatten the image if you won't need to work with the extra layers. Otherwise use Export As Jpeg to save a copy. The message gives an option to turn it off in the future, but I prefer to see it in case I have forgotten to flatten it.