[2020] Industrial buildings without the zone?

Actually I would suggest Plop The Growables instead. Ploppable RICO is designed to add functionality to parks and unique buildings, and it can make growables act a little weird. Plop The Growables is designed to let you place growable buildings by hand and make them more robust, so they don't disappear.

https://steamcommunity.com/sharedfiles/filedetails/?id=924884948&searchtext=plop+the+growables

Buildings placed with both mods will still need road access as they are still functional buildings. If you just want them to be decorative and prefer they have no function at all, then it might be worth looking into Procedural Objects instead.

https://steamcommunity.com/sharedfiles/filedetails/?id=1094334744&searchtext=procedural+objects