Writer keyboard shortcuts
Screenshots are almost useless to characterise bad behaviour, all the more when View>Formatting Marks are not enabled (it would give some hint about the formatting).
Edit your question (be kind to contributors, sparing them the pain of going through a wealth of comments to build a synthesis of the question) to add minimum technical information: OS name, LO version and perhaps save format.
What is your shortcut? A link to a built-in command, a character or paragraph style application or a trigger for user macros? Attach your file for analysis.
Characters don’t appear per spontaneous generation. They have been added by some explicit mechanism (by a user macro?)
The best and most reliable method to apply customisation to document elements is with styles. You can then attach a shortcut to frequently used styles. Don’t do this with macros. Keep them for really complex and unusual tasks.
I add that macros frequently apply direct formatting which will always play some nasty trick on your back.
Alt+[Numpad] are hard coded into a fundamental layer of Windows since long ago. They cannot be changed unless Microsoft make the changes.
I agree it is hugely annoying but it is just one of the costs of using Windows.
External link to similar question windows - Turn off one-digit Alt codes - Super User
Wikipedia (history) touches on it Alt code - Wikipedia