Hello Peleg D,
I’m Gunasekar and I will be happy to help you with your question, I am a Microsoft consumer like you.
This feature "Customize keyboard shortcuts only works on Word for Microsoft 365 Word 2021 Word 2019 Word 2016 Word 2013 Word 2010 editions". The best you can do (without an add-in) is to add commands to the Quick Access Toolbar. If an icon is in the 5th position from the left, Alt + 5 will activate it.
To customize keyboard shortcuts on PowerPoint, you will need to use an add-in : OfficeOne Shortcut Manager 8 for PowerPoint. This issue was already discussed in a similar thread,
https://answers.microsoft.com/thread/9b894f01-6ece-4abc-b13a-0cc5c1730965
(You can also download the add-in separately from their official website)
I hope this information helps. If you have any questions, please let me know and I’ll be glad to assist you further.
Best regards,
Gunasekar N