You can't dirty flash from one android version to another - need clean flash and probably Format data. If you have an external sd card pull it out, flash the rom and then pull it again in phone.
Snapdragon 660 supports 1080p video up to 120fps. It's up to Xiaomi to implement these features or not. My Mi note 3 also has the mentioned cpu but the camera can shoot only 1080/30fps
Xiaomi.eu rom, Lineage 16 - you can check the Mi note 3 page on xda. There you will find info about roms and guides https://forum.xda-developers.com/mi-note-3
Restart phone in TWRP. Go to Wipe section and you will see an option FORMAT DATA, click on it and type yes to confirm the erasure. Restart the phone back to recovery, copy eu rom to phone and install it, wipe Cache and dalvik and reboot to system.
Download Aida64 app from Google play store and in Sensor section check if it displays values for the other sensors. If not the persist partition may got corrupt.
Eanble Usb debuggings and connect the phone to pc. Open the folder where adb is installed and press Shift key, hold it and then right click and choose open command window here. Then type thease commands cosequtevely:
adb devices
adb reboot bootloader
fastboot flash recovery twrp.img
fastboot...
The Updater app is buggy. Try to press the Download button for at least 15 seconds and the download should start. If not just download the rom manually from the download section in the site, reboot to Twrp and install it, clear Dalvik and Cache and reboot. Done.