@The-Hitman:
Exactly what you’re asking — to highlight all the text following the equals signs and then sort on that — is, to the best of my knowledge, not possible. Since the equals signs don’t line up, you’d be creating a multiple selection rather than a rectangular selection, and the sort functions don’t work on multiple selections. So even if you got your selection, you wouldn’t be able to sort it.
However, there are ways to accomplish what you want. One thing isn’t quite clear to me: in your example, both the numbers in brackets after the capital Ms at the beginning of each line and text to the right of the equals signs are in ascending order — but presumably, if you need to sort, the text parts don’t start out in ascending order. Do you want to sort the text part of the lines only, so that the numbers stay in order and the text gets associated with different numbers? Or are the numbers supposed to move with their associated text, so that the text will be in order but the numbers will no longer be in order?
Either way, it can be done without too much difficulty. The key step is to temporarily right-justify all the numbers, so the equals signs line up:
M[ 97]=DM-Elysium:1
M[ 98]=DM-Enemyatthegates:2
M[ 99]=DM-EternalWinter:2
M[100]=DM-FactoryTown:3
M[101]=DM-Fastfood:1
M[102]=DM-FAT-Musashi][:2
You can do that by creating a zero-width column selection in front of the numbers from 10 to 99 and typing a space, and similarly adding two spaces before the single digit numbers; or you can use regular expression replacement to add the blanks. (With either method, you could also add zeros instead of blanks if you like those better.)
You might not know how to do either of those things. If you don’t, please first try reading the sections in the online manual titled Selection modes & Column Editor and Regular Expressions. (Sorry to be indirect about answering your question, but these are basic skills for using Notepad++ effectively. It is worth learning how these things work so you’ll know how to solve other problems in the future.)
Once you have the equals signs lined up, you can create a zero-width column selection just after the equal signs and use one of the sort commands to sort the result. (If you wanted the numbers to stay in order rather than move with the associated text, just use Edit | Column Editor… to renumber after sorting.) Then use regular expression replacement to remove the unwanted blanks.
There is an alternative method, using the Columns++ plugin which is available in the Plugins Admin. Custom sorts in Columns++ allow you to specify a regular expression which matches the sort key in each line; so, instead of manipulating the lines to line up the sort fields, you’d use an expression like =.* to identify the sort key. Unless you already have that plugin installed, this would probably be more complicated for your case than the method described above, but it is an approach that could be useful in similar but more complex cases (or for those who already use that plugin).