Direct link to announcement instead of low effort spam blog: https://www.ubisoft.com/en-gb/game/for-honor/news-updates/4WKJhG6v6C9sbCOZkFZ6wG/ranked-faq

Relevant part:

Competitive Update

Warriors, we are happy to announce that For Honor’s competitive experience is leveling up with the launch of Ranked Dominion and the rework of Ranked Duel.

The chance to prove yourself on a global level is here!

To reinforce a fair competitive environment, the team is introducing additional player safety measures. We are removing For Honor from the Linux platform to ensure a safer environment for our players as we cannot meaningfully deploy protection on this platform. This means that For Honor will no longer be playable on Steam Deck starting September 10th. We will continue to investigate different ways to improve our anti-cheat with the possibility of reopening the platform in the future.