There are lots of options for roleplayers who want to bring the Witcher to the table in the meantime, of various levels of complexity. There’s On the Path for something fun and streamlined, or Vaesen and Ironsworn for a bit more meat. You could use Monster of the Week or Bump in the Dark if you’re willing to move the setting into a more Witchery direction.
And if you’d rather stick with a system you’re more familiar with, there are supplements like Into the Wyrd and Wild or The Perilous Wilds that allow you to put your players through dangerous evirons on the trail of unique monsters.