Various Discord servers I am in have made announcements mentioning Steam being "Hacked" today. As usual it isn't currently confirmed and no legitimate proof has been verified by reputable sources.
If it were to be confirmed from the information in the post, it is at worse a regular data breach from a third party who connects to steam and the only people who would be at risk(as they always are) are people who don't have 2FA(Steam Guard) enabled.
Regardless of the validity of this breach I would still recommend to enable Steam Guard on your account if you have not done so.
The claims come from a LinkedIn account named: "Underdark.ai", which raises additional red flags as anything AI related tends to be unreliable.