[Huawei P Smart ROMs, Kernels, Recoveries, & Other ] SleepyMoritz:
I managed to install Lineage OS without encountering bootloops or any other problems following this steps closely (Failing one step usually means starting over...) . I'm using the same phone (FIG-LX1-C432) and got it working perfectly. I hope I can help somebody by posting this. If you have any further questions, feel free to contact me.

I'm not responsible for any kind of bricked device, void warranty or lost data. Backup everything beforehand.

Unlocked bootloader is needed ofc.

Flash (latest) MIUI 9 for your device. I used dload method (extracting update zip and loading files to sd card, update using SD Card Upgrade from Phone Manufacture Mode or holding volume up, volume down and power when powering device on). MIUI 9 is required to flash Lineage OS, otherwise it'll end up in a bootloop.

Unlock bootloader again if neccessary (sometimes EMUI Update locks bootloader, but you can use the same bootloader unlock code you already used to unlock it again, enable developer options in settings and enable oem unlock, then fastboot the device and use fastboot oem unlock).

With bootloader unlocked and device set up using EMUI 9, flash twrp-3.4.0.0-v1-figo-haky86.img using fastboot flash recovery_ramdisk . Do not turn the device off or disconnect it yet.

Reboot directly to TWRP. This is neccessary because after booting to system, EMUI will damage TWRP and therefore bootloop the device

Type fastboot reboot in cmd, don't enter yet.

Hold your phone in one hand pressing volume up and power at the same time.

Press enter on the keyboard, phone will reboot.

Instantly disconnect the usb cable from the phone while holding the buttons volume up and power.

Phone will reboot one more time. Hold the buttons until bootloader warning appears. Remove your fingers from the buttons. Phone will boot to twrp.

in TWRP, wipe System, Cache, Dalvik, Data, Internal Storage (Be sure to backup all data before).

Flash Lineage OS Rom either from ADB Sideload or from sd card. Both worked for me.

To flash gapps, resizing system partition is needed. Go to wipe, mark only system partition, go to repair or change file system and choose resize file system. Without resizing, phone will end up in bootloop.

Extra Warning for Gapps: Be sure to flash a gapps package that contains "android system webview". This is neccessary to login to your google account. If Googles "android system webview " is not installed. setup will crash and you won't be able to enter your phone / use your google account. I'm pretty sure this is a lineage os bug, because Lineage OS has its own webview, its just not working. Until it works for account login, you'll have to stick with Googles Webview Version.

Flash Gapps.

In TWRP, go to the reboot section. Connect phone to PC and choose reboot to bootloader. Phone should reboot to fastbood mode.

Flash Stock Recovery using the same method used for twrp. (Step 3)

Reboot to Stock recovery using the same method used when rebooting to twrp. (Step 4!)

In EMUI Recovery, choose factory reset option, accept every warning and do factory reset.

Choose reboot / reboot to system. Phone should boot to Lineage OS now.

This worked out for me. Lineage OS 16 by haky is amazing. It's super smooth and so much better than MIUI in my opinion. Really happy with the rom.

Sadly, updating Lineage OS didn't work for me yet. Using the official updater reboots the phone to recovery. EMUI Recovery shows an error message and reboots. Flashing TWRP, applying update and flashing stock recovery led to a bootloop. Is there any official / working way to update the device, besides the Lineage OS Website? Maybe Haky can help me out here...