Please follow the guide at https://faq.elytra.app/2022/smart-folders/ on creating a new smart folder.
Smart Folders match article titles when you use a title rule. The text is matched using case-insensitive rules, i.e., the rule galaxy will match Galaxy, galaxy, GALAXY and all such variations.
Smart Folders match feeds from specific folders. You can choose to either include or exclude feeds from specific folders.
You can combine the above three rules to create complex sets. These are evaluated extremely quickly and efficiently providing a smooth and seamless experience of automatically categorising articles into Smart Folders.
Keywords are not presently available as an option because of how they are optimised for SEO and do not effectively reflect the content of articles. I hope this changes in the near future so keywords can also be introduced as an option.