@vivek-viv ,
Unfortunately, there are an unknown number of “programming languages” or “data file languages” in the world, and no text editor can syntax-highlight 100% of them out-of-the box.
Apex is not available in the syntax-highlighter library that Notepad++ uses, and until it is, it will never be in the upper portion of the Language list.
To get it added: A feature request would have to be put into Lexilla, and then the Lexilla team, or external volunteer, would have to code up that lexer, and they would have to accept it, bundle it with the library; then Notepad++ could update to use a version with that, and then and only then, Notepad++ could be updated to enable and list the Apex language in the default menu. I’m not saying it’s impossible… just that it’s not likely to be fast. If Apex were similar enough to another language, then, in theory, the Apex language could be mapped to use the that existing language’s lexer, but given its own list of keywords.
However, Notepad++ has the User Defined Language (“UDL”) feature, which allows you to define a keyword-based syntax highlighting – so you can put in various lists of keywords, operators, folding-keywords, and delimiter pairs, and get it to do a reasonable job of highlighting simple syntax in your language.
The User Defined Language page, and all the UDL > pages in the manual’s table of contents below it, describe how to use the UDL system.
There’s also a community-contributed User Defined Language Collection, where people can share UDL definitions that they’ve made, or find ones to use for themselves. I don’t see Apex there… but if you created one, you could share it there, so that other Apex users
I did a quick search, and if this is the Apex you are talking about, then it looks similar to YAML (builtin) – so maybe trying to use the YAML lexer might be an initial workaround. And google search AI tells me that the HAML uses a similar structure – there is a UDL in the Collection for HAML, so you might be able to use that as a reference for how to get something like what you want for Apex. No guarantees, but it’s a starting point…