[Verizon HTC One (M9)] imonxda:
Well, I guess I wasn't very clear, sometimes I tend to babble. If I'm posting stuff you already know, sorry, its better not to assume you know something then find out later when something goes wrong that you didn't know, right?

1. Install HTC drivers: https://androidfilehost.com/?fid=24269982087005596.

https://xdaforums.com/t/tool-minimal-adb-and-fastboot-2-9-18.2317790/ install adb & fastboot, pay attention to the location that you install to. Open a command prompt in this directory to use.

2. https://androidfilehost.com/?fid=24341993505161791 download the htc_fastboot.exe, rename it to fastboot.exe, then paste it in the same directory where you installed adb & fastboot and overwrite the existing fastboot.exe.

3. https://twrp.me/htc/htconem9.html find download section and get v3.1.1.0, then follow fastboot install instructions on this page while M9 is in Download Mode and connected to your PC w/ USB. The key command is, run command prompt in the adb/fastboot directory:

fastboot flash recovery "full path to downloaded TWRP.img file"

4. command: fastboot reboot-bootloader then boot to recovery = TWRP. Create backup of the boot partition make sure to uncheck the Compression in options tab of the create backup screen.

5. Normal boot your phone and download and install latest Magisk apk https://github.com/topjohnwu/Magisk/releases

6. Open Magisk Manager app on the phone hit Install>'Select a file' option and choose the boot partition backup file located SDCARD>TWRP>BACKUPS>'your backup name'>boot.emmc.win , pay attention Magisk will show the location of new patched boot image, usually in SDCARD>Download.

7. Developer Options in settings (tap about>build number a few times to enable), enable USB Debugging, then connect Phone w/ USB to PC. Copy the new patched boot from SDCARD>Download to your PC.

8. connect phone w/ USB to PC, command: fastboot reboot-bootloader , then Boot to Download Mode, , run command in adb/fastboot directory while in Download Mode:

fastboot flash boot "full path to new Magisk-patched boot .img file you copied from your phone"

9. Normal reboot, open Magisk Manager App, and it may ask to reboot, then set your root settings in Magisk preferences.

10. https://xdaforums.com/t/...loader-without-htcdev-s-off-required.3092036/ open command in adb/fastboot directory and follow instructions in that thread while connected to PC with USB to unlock bootloader.

At this point you have unlocked the bootloader. You are now ready to install a custom rom, custom kernel etc. On my phone I had to use WIPE>FORMAT DATA in TWRP, it will make you type out 'yes', the normal DATA partition wipe was not enough to get rid of data encryption to allow installing custom roms, THIS WILL WIPE OUT ALL YOUR INTERNAL STORAGE, and you must reboot TWRP after for new DATA partition to work. Most custom Sense roms come with some root solution, but my experience has been poor with installing root (Magisk or SuperSU) from the Aroma installer for a rom, I always try to skip root install in Aroma, then as soon as rom installation is finished, say NO to reboot, then flash a root zip, as I said before, you can rename Magisk.apk installer to Magisk.zip, then flash it in TWRP to root any rom/kernel.

Good luck