FSRS-5 is still in alpha stage, so you could only use it via the custom scheduling script.
Here is the tutorial: https://github.com/open-spaced-repetition/fsrs4anki/blob/main/docs/tutorial2.md
Release files
- Scheduler: fsrs4anki_scheduler.js
- For Qt5 version: fsrs4anki_scheduler_qt5.js
- Optimizer: fsrs4anki_optimizer.ipynb
What's Changed
- Update to FSRS-5 by @L-M-Sherlock in #664
Full Changelog: v4.15.2...v5.0.0