I finally managed to install the ROM yesterday using differents instructions.
Here is how I did it if you are struggling to install like me at the beginning (or maybe there was just a fix in between, I don't know).
Before doing anything, the usual, you might want to take some precautions: do backups and remove the SD card from your device before loosing anything. What follows is going to format your internal storage.
Please respond if anything is wrong in here of if you have some details to add.
My installation was done from Android 10 stock 52.1.A.0.618. You can install it from a program called "Emma" from Sony.
You will first need to extract "payload.bin" from the .zip ROM file you have downloaded (Pixel Experience).
You will then need to use a program called "payload dumper" to get the files you'll be installing with fastboot afterwards from the payload.bin you just extracted. (expect around 6GB of files)
You will also need to extract "SW_binaries.img" from the most recent binaries .zip, which you can download on Sony's website.
In your command prompt you will need to do the following:
> fastboot flash boot boot.img
> fastboot flash dtbo dtbo.img
> fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img
> fastboot flash system system.img
> fastboot flash vendor vendor.img
> fastboot flash oem_a SW_binaries_for_Xperia_Android_10.0.7.1_r1_v6_tama.img
> fastboot flash oem_b SW_binaries_for_Xperia_Android_10.0.7.1_r1_v6_tama.img
Some things to keep in mind and which I would have liked to be aware of :
If you can't use --disable-verity and/or --disable-verification, try to launch your terminal from the folder of your most recent platform tools. It seems like they don't exist in some adb installers.
Flashing the files to your phone may take a long while to start. Just be patient.
You may see a "Invalid sparse file format at header magi" message at some point. I am not sure what it means (tell me if you know) but I got it and my phone is working just fine right now.
If you see a Google logo after the Sony logo, it means you probably succeeded.
After installing, my phone bootlooped two times. It then showed me a menu where I could format some data. I did it and after that it took a while to boot the first time but finally worked.
Here are the builds I am currently testing on my Xperia XZ2 Compact (H8324 REV6):
I will try to tell you about the bugs and issues I may face in the next few days, but right now the ROM is feeling way snappier than Sony's stock Android 10 ROM in my opinion and the animations are gorgeous.