In order to use Templates, you need a theme that is FSE (Full Site Editing) compatible.
There are many such themes available and Cwicly has it’s own bare bones theme / child theme.
Personally, I prefer to let Cwicly do the heavy lifting and build reusable resources with it, rather than relying on themes which are less flexible and extensible, but it is based on your preference.
So far with Cwicly there has always been a creative way to achieve what we’ve needed to do without needing to compromise the design or functionality, which has not been the case in the past with most themes, even the ones packed with features.