Sometimes there is no 'Close Button' to close patch notes.
Open the Launcher
Go to the Minecraft section, the Minecraft Dungeons section, or the What's New in the Launcher
Go to Patch Notes
Open a Patch Note
❌ There is no longer an X to close the Patch Note
When the close button does not appear, you need to press esc. This is not ideal as it sometimes requires you to press esc multiple times, and this does not always work; meaning you sometimes need to quit the launcher and re-open it.
I cannot reproduce. A close button is shown for me on Dungeons patch notes.