In find instead use the string \.5 and uncheck Whole word.
In the documentation it is stated that .NET regular expressions ( .NET Regular Expressions - .NET | Microsoft Learn ) are supported. Escaping the dot will make it a regular expression. It means that it finds a literal dot and a 5. If you want to ensure it finds only .5 and not .55 or 5.5 use ^\.5$. ^ means start of the line $ means end of the line.