Jut had a bit of a panic whilst trying to flash Pixel OS.
So good news is that I was able to successfully unlock bootloader but that's when it went downhill. So I followed the steps
here and downloaded the files I needed (which included flashing the TWRP in the post rather than the official one) and put them on the root of my "Internal Storage". Using adb I was able to flash recovery to the TWRP provided and then booted into it. All good. I then noticed that in TWRP my internal storage was 0mb and it wouldn't let me view the files to flash the ROM etc. A bit of googling and I found
this guide. Followed it and after step 8 my internal storage was somehow wiped (I'm 99% I formatted Data and not Internal Storage). Oh ****. Booting back into fastboot made the phone show in Windows but Internal Storage was indeed blank and I couldn't copy any files to it or view any files on it. At this point I had a bricked phone as the phoned failed to boot into anything other than TWRP.
I then thought I would try flashing the official ROM back to my phone to fix it and worry about Pixel OS another time. Have done it before with other phones when I've tried custom ROMs but then put it back onto MIUI either due to problems or due to selling phone. Downloaded the official fastboot MIUI rom and the miui rom flashing tool. However it wouldn't flash and kept coming up with an error. saying it couldn't find a file or folder (presumably due to Internal Storage being empty) Oh **** again. Anyway managed to mess on in TWRP in fastboot mode (Think I had to turn on ADB mode) which made it work. Phew. After what seemed like ages the phone finally booted into MIUI and I have a working phone again.
I was stressed
Anyway I downloaded the EU rom (V14.0.2.0.TKFEUXM) and it was bloated with loads of Games and Apps that I can't remember having there the last time. All removable but they really shouldn't bundle them into the ROM. What I've noticed is that my phone is reporting I'm using a Global ROM. Shouldn't it say Europe? I can't remember what my phone said before trying to put the custom ROM on it. MIUI version is listed as what I downloaded.
I may yet give flashing Pixel Os another go but not today...