Why do some characters are not displaying correctly in this website? If I go to this website: https://www.w3schools.com/charsets/ref_utf_misc_symbols.asp I can see some of the first glyphs, but later down the page most are missing.

In their place, I can only see the "missing character" glyph, which looks like an empty block.

What does this happen? Am I missing some font? Should I install some extra font in my Mac OS?

Is this the expected behavior of my OS, or is it a bug?

By the way, the above website's glyphs render just fine in any other OS I've tried (both Linux and Windows). 

Browser: Latest Chrome
OS version: High Sierra 10.13.6
You presumably need to download and add a font.  Try Symbola.

If you have an iOS device, I think you should find the same behavior.  Apple's supplied fonts do not cover all of Unicode, which has well over 100,000 characters.

To check whether your MacOS has a font covering a specific character, you can open Character Viewer (Edit > Emoji and Symbols), select Unicode, and find the hex number.