Hiya,
The adult patch is all grown up now, and is a full-fledged Steam DLC. Still free. You can grab it at https://store.steampowered.com/app/943720/Highway_Blossoms__18_Adult_Only_Content/
This is the exact same as the 18+ patch that we host on our website, so if you've gotten it from there, you don't need to change anything. There's no content in the Steam DLC version that isn't available in the old patch. You can continue to use that version if you'd like, or you can switch to using the official release.
If you weren't aware of the adult patch, well, as its store page says, it adds two uncensored sex scenes towards the end of the game. The illustrations are by Weee/Raemz.
Want to know if you've already passed where the scenes would've occurred? Both take place After the Las Vegas section of the game. One is right after visiting the World's Tallest Thermometer, one is after Amber and Marina make up from their argument, right before they go to the music festival.
It probably goes without saying, but you need to be 18 years or older to download and play the adult patch.
Have fun!