Rocket Chat search supports the use of "regular expressions", the benefits of which are great search flexibility and the ability to search chat entries in any language, even ones which are traditionally a challenge for search (e.g. "CJK" languages - Chinese, Japanese, Korean).
Regular expressions are a deep, but admittedly geeky topic. The flexibility of "regex" search increases as you learn more about how to write regex patterns, but if you learn just a couple of simple patterns, you can benefit right away.
Let's see a few simple examples that you can try.