Praise the (modding) sun.
FromSoftware games always have an interesting life on PC. They're released, the community grumbles about a lack of basic features on PC, and then eventually a modder fixes it all two or three weeks after release. Sekiro is no different: The game launched without a borderless fullscreen mode, the frame rate was locked to 60, there was no support for ultrawide resolutions, or support for high refresh rate monitors.
The patcher, which you have to launch every time before playing Sekiro, enables custom frame rate locks, borderless windowed mode, support for G-SYNC and Freesync in all windowed/borderless/fullscreen modes, and the ability to adjust the game and player speed. The latter is kind of interesting, if only because you can control those sliders independently. If you were finding Sekiro too hard, you could speed the player up (or enemies down). Alternatively, you could just double the speed of the whole game.
If you really want to be a masochist, you can even check an option that logs all kills and deaths to a text file, which you can then add as an overlay in OBS or Xsplit:
More details on the mod can be found here.