The official version is available on Steam . While it is usually a paid game, you can check for seasonal sales or use the OTAKU Plan website for news on bundles.
There are a few different things you might be looking for under the name Below are the details for the most likely matches, including where to find them for free or at the best price. 🏰 Home & Dungeon (Town-Building RPG) Home and Dungeon Free Download
You can sometimes find free "quickstart" rules or community versions on itch.io. The official version is available on Steam