I think it should be fairly trivial to do with Python and a calendar library, you’d just have to go through the input entries, keep the ones with the properties you like and dump those to the output.
I’m not well versed in Python either but I had a specific calendar problem once — had to clear a calendar storage that went back years and the provider’s UI didn’t let you delete the base calendar — and after looking it up it was a few lines of Python.
That’s probably why you don’t find established tools because every person who runs into this stuff has a super specific need.