Possible to install unbranded android on HTC ONE? I am so sick of stone old android version HTC installed on my smartphone. While the phone is still super after several years HTC do update the Software anymore. So I d like to remove the branded garbage and install a fresh secure android on my device. Can some one point me to good docs or tell whether this is possible?

How to find device model number or version on the phone?
Where or how to find the correct image for my phone and how to install it?
It would be either very difficult or not possible at all.
Since Android is an Operating System, it is designed to fit varieties of devices, which differ in all kinds of modules that require specific drivers for themselves. Therefore if you want to create a clean Android build you must gather those drivers (and some additional configurations) to make it work properly on your device. Meanwhile, almost all 3rd-party ROMs are either manipulated from the official ones, or have extra configurations pre-applied, which both don't meet your requirement.