@Billylin0704
I totally agree, KitKat, though long dead, was the best Android experience on the M8 by far. I have been collecting roms for the M8, presently I have the zip installers for around 200+ roms, most of them are KK roms. I have installed about 75 roms on my external SD using MultiRom, and they all work, I can boot all of them and most of them have all features working and no major bugs or problems. If you or anyone else is still interested I can hook you up with what I got. I also have a bunch of kernels with k-exec patch for Sense, GPE and AOSP for Android 4.4.2 up to Android 8.1!
I still use Viper 4.4.4 as my go-to rom, even though many apps are no longer supporting KK, I have also apk installers for the last kitkat compatible versions, or I can use the last still working browser for web-based access to stuff like online banking, or other online services for which the apps no longer are available on KK. I know this was posted last year, I think no one gives a crap anymore, but I still do

Oh, I should mention, I'm on Verizon, so all roms and kernels support Verizon, all other carriers are not tested and most roms/kernels are NOT compatible with other carriers.