With shift flashing and rooting does not void warranty. With fairphone at least rooting does, don`t know about flashing tho. There is a community for degoogleing for sure tho.
Written from my fairphone after the Wifi chip on my shift died after 2.5 Years and it was to expensive to fix.
https://forum.fairphone.com/t/does-rooting-void-warranty-for-fairphone-4/82441/16
I had this thread in mind however seems like I was partially wrong. But there does not seem to be a definitive answer.
Should have read the thread further the first time :D Sorry about that