I'd love to see some styles built in such as h1, h2, h3, h4, block quote, and code. (Not terribly dissimilar to this forum's formatting tools.) They could be simple styles with toolbar buttons and shortcuts, but that would speed up my note taking processes. Having to stop to format a subhead and then format back to a paragraph as I type severely slows down my notes, which mean I occasionally miss things in person or have to rewind videos — or I have a mess to clean up later.
Thankfully, some additional formatting (superscript, subscript, strike through, etc.) is available in the Format menu and includes shortcuts.
FYI: The highlight issue is discussed here from 2013:
Interestingly, if you type in Word and highlight the text using multiple colors and then copy and paste that into Evernote, the highlight colors are retained. So, Evernote is capable of it. It's not accessible to users. (If you edit the copied text, the highlighting gets wonky though, which is far worse.)