How do I install the full version of Windows 10 on a Lumia 950XL?

Check on Telegram: there is Channel for Lumia 950XL with all the explanations on installing Windows 10 on this mobile.

I've already tried using the WPInternals program but it didn't get me anywhere other than getting stuck in flash mode which I was able to get out of by using the WP Internals program to re-install Windows 10 Mobile which made me loose all of the data on my phone because I was stupid enough to not back up all my data to my PC. 

Upon recently looking at this if you read enough of relevant resources you will find that FFU file downloaded using WPInternals is slightly smaller in size than one downloaded from https://www.lumiafirmware.com/model/RM-1085 so replace the FFU file in Windows(C):/ProgramData/WPInternals/Repository/RM-1085 with one from this source (RM-1085_1078.0053.10586.134169.034EA6_retail_prod_signed.ffu). This removed all the "Bad GPT" errors produced by WPInternals following initial infamous Windows "Bitlocker recovery key" screen due to Samsung eMMC requiring use of Windows Device Recovery Tool to recover device:https://support.microsoft.com/en-in/help/12379/windows-10-mobile-device-recovery-tool-faq

This time around progressed beyond flashing "Part 1" and rebooted into "Mass Storage" mode when all system files become visible in Explorer and allows flashing of "Part 2" to proceed with result of bootloader being unlocked.

Think that you will also find that things have progressed a bit further during last few months:https://github.com/WOA-Project/WOA-Deployer-Lumia although it looks like Camera is always going to be a stumbling block unfortunately.

Look here:

https://forums.windowscentral.com/windows-10-mobile/475274-guide-installing-full-windows-10-arm64-lumia-950-xl.html

I'm not sure if it is worth the the time, effort and energy only because it could be just too small to view and not everything will work IMHO.

That said, it is a good read and if you are somewhat diligent in process it might be fun to try.

This link is a good read as well:

https://pureinfotech.com/install-windows-10-lumia-950-phone/

Interestingly enough I was reading this the other day and it did spark an interest. After spending time on it, I decided to not try it because it just did not seem it was going to be a smooth install and I was not quite ready to give up use of my 950XL as an emergency device in case my daily device was lost or broken. If you do try it again, let me know how you make out. Issues with charging after the install and the few things that won't work scared me away.

Good luck!!

I installed it last month and except for the camera and battery life, I am pleasantly surprised by the performance. The devs did an amazing job.

Oh wow, thanks! I will definitely try it out and it should hopefully work