Duration shiftTo seems to produce wrong result when upgrading to latest

[HarryDavisgithub]

I am trying to get the difference between two days as a ISO 8601 Duration string. I want this to take into account leap years. I recently upgraded from luxon: "^1.26.0", to 3.4.4 and the code in function1 no longer gave the same result as it did before.

I would expect "2020-01-01" to "2050-01-01" to give P30Y8D

Function2 is my attempt at a solution but does not seem to take into account leap years.

https://codesandbox.io/p/sandbox/boring-sound-h2r35k?file=%2Fsrc%2Findex.ts

Please let me know if anyone has any suggestions, or if my logic/thinking is wrong here.
Thanks!