If that's Chrome on Windows 10, then the short answer is: You need a Chrome extension, otherwise you can't.
There is no universal way, because chrome maps Alt + d, e and f to do things which stops you entering a hexadecimal unicode in with the 'universal' windows Alt+ num pad trick (which may itself require a registry key to work).
Worse, you may find (as I did) that using the alt-numpad code with a leading 0 for a unicode decimal entry also doesn't work (because it is input language specific).
The most universal way is to google for the name of the character you want, plus 'utf-8', and copy/paste it when you see it. Unsatisfying? Yes.
Else you can enter the code you know into another application, and copy/paste it into chrome. Wordpad is good - type the code in, and then hit alt-x.
If you want to avoid copy/pasting, then you need a chrome extension.
The most trivial is the 'Unicode Input' extension, which makes the insert key work like alt-x does in wordpad. There are many others also.
Another is the 'wasavi' chrome extension, which allows you to quickly drop into what behaves like a 'vim' in any text entry field on a web page.
Then, you can (in vim's insert mode) type ctrl-v, then u
to put it into unicode entry mode, then you can finally type your unicode hex code in however you like.
Either of these mean you can enter unicode into chrome, like you want to, without having to install another windows application or mess with the registry.
Even if you cannot install software (don't have admin rights), you will be able to add the extension to your chrome account, and use it wherever you log in, on any platform. (This should also work in edge, but with your Microsoft account).
If you can touch-type, you should seriously consider learning how to drive vim. Given that you want to insert utf-8 characters by hex codes, you probably are a good match for it, and will find it useful.