It may be that the side scrolling template hasn’t been updated to the latest version of the engine.
Your option is to install an older version of the engine, or re-create the template yourself.
Worst case, you can install 4.27 and use the templates there. There have been some changes up to version 5.3, but most of the 4.27 broad strokes are still useful. (The biggest change is probably the new input system, but learning the old one, and then watching a youtube video for how to upgrade, is not that bad of a path.)
(Just checked 5.x templates, and, yes, they dropped the 2D templates in 5.x. 4.27 has it, though.)