Can you take a screen shot of what you are seeing and upload it to an image hosting website to link the image here?
(edit out any visible account or character info)
I just checked on my system the Windows PC version of the Launcher (in both old and new UI formats) and the loading screens in game.
I see no "Steam" anywhere, except the launcher link to the article about the Steam Version Linking in the news Topics section:
"* 02/09/2022 Introducing Steam Version Account Linking" which click opens the FF14 website to that Topic.
I do not have any Steam software on PC nor have any Steam accounts, and I have never seen any sort of advertising in the game loading screens, ever.