I can’t really say anything about exclusion tags, but there are some workarounds to the issues you’ve mentioned.
To prevent adult content from appearing in search, you can go to “Settings” -> “Profile” and untick the following option:
[ ] Show content marked as adult in search & browse
Keep in mind this will hide all games that the developer has marked as adult-only> Apart from ones with sexual content, this also include games with extreme violence and similar themes, that are not for children.
I’m not sure what you mean by “demos”. Are you referring to games that only have a demo but not a full version? In that case there should be a filter somewhere for games marked as complete, I believe.
Hope this helps