I've been using Steam as an adult for the last two decades. I have hundreds of games in my library. I've never seen one porn title recommended to me or while browsing the site.
The lack of an opt-out filter was an issue that Collective Shout supposedly campaigned for that went through Steam Labs and was them implemented for everyone circa 2020.
I had to specifically block those from being shown, they were all over for me. I don't have any issue with them, but my kids use my steam deck, and game on my pc, and I didn't want them seeing those.
Steam also has extensive parental controls: https://help.steampowered.com/en/faqs/view/054C-3167-DD7F-49...