I have just checked Window > Macro Library in the Keyboard Maestro Editor, and the Rotate 180° filter is not listed.
The filter (and other image filters) are mentioned in this post from 2019. "All nineteen (19) macros were installed in the Clipboard Filters Group, which I did not create."
So... either @Airy and I got the Rotate 180° filter and other image filters from the same long-forgotten source, or those filters used to ship with Keyboard Maestro but no longer do. The above comment from 2019 suggests the latter.
Update:
"There are 21 filters included with every Keyboard Maestro installation:
...
- Rotate 180?? [sic]
source: Keyboard Maestro Blog on cryan.com , December 22, 2021.
The acid test would be to create a new user account on one's Mac and reinstall KM (but I am using Venturda and the last time I did that it lead to YA MacOS bug time sink so I am not volunteering 
).