I've checked that being logged in and having an adblocker doesn't make all 18+ clickthroughs disappear.
I do not understand this. What is a clickthrough? What have adblockers to do with this?! There are no ads on itch! Do you use an adblocker to shield you from adult content or what?!
If you select tag adult to browse, you will see adult games. If you do not, you need to log in and have the adult check box activated. Otherwise you will not see things marked as nsfw in search or browse. You cannot even search for creator's names in search, that have any adult projects.
Also, if that setting is deactivated, you still have to say that you are an adult if you visit a page, should you come across a game link by other means.
( ) Show content marked as adult in search & browse
Check this setting in your account's setting.
Also, if you did previously visit such a link, there is a dialoge
Are you 18 years of age or older?
( )Remember my setting for this browser
That setting will stay. It is a cookie probably.
I don't really want to go back to said game page in order to report it
As of now I will assume that you saw a game that was in fact not marked as nsfw. Because if you told itch you are ok with adult content, you should not complain. Just because you think it is offensive, does not make it so.
It happens. Devs here are mostly amateurs, they might have forgotten. Also, there are scammers uploading malware. Often disguised as adult games. But they usually do mark it as nsfw, precisly because they will get reported for having an unmarked nsfw game otherwise.
So if you want to report it, but do not want to use the report link, just go to your browser history, copy the link and contact support (read: write an email to support) with that link and your findings. If it was not a mistake by the developer, it probably was malware.