I’ve long been rather triggered by the use of the term “halvening” rather than halving, so I’m with you! Despite the fact that people can call it what they like and I shouldn’t care.

However.. having googled it, it appears halven is a word with more historic credibility than I thought

https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED19880#:~:text=(a)%20To%20divide%20(sth,number)%2C%20divide%20by%20two.