It can be very useful to use a prefix when naming things, for example when you have many similar variables that you need to easily tell apart or a list of files of different kinds so you can group them together alphabetically.
A great example of this is found in the SvelteKit file route naming conventions, where all files related to routing are prefixed with a + so they all appear together at the top in a folder.
A time where name prefixes are not useful is when differentiating variable types, for example prefixing interfaces with I (aka Hungarian notation). This is not useful as my editor should be able to provide me this information very clearly. In the case of interfaces, VS Code highlights them in a special color, and will vomit errors if you misuse an interface as a variable. This convention is a relic of the days of yore, before decent language servers and usable IDEs. If we ever start writing a project in C++ I am willing to reconsider this stance.
Yes I know this is a convention in C# but it is not in TypeScript, and in the past has been specifically disavowed by the TypeScript team in the past (which is saying a lot since both languages were designed by the same guy):
Naming Conventions
In general, do not prefix interfaces with I (e.g. IColor). Because the concept of an interface in TypeScript is much more broad than in C# or Java, the IFoo naming convention is not broadly useful.
TypeScript handbook, 2015
If your editor can’t easily show you what type your variable is, you have made a mistake already.