tilde over u

Sorry about that (teaches me to wear my glasses :-) ). The character viewer seems to do the trick (see below). Once you've found the character of interest (best to add it to favourites), you can double click on it to enter it at the insertion point: -> ũ

Hope this helps.

- Pie Lover

In System Preferences > Keyboard > Text, you add an arbitrary trigger string (e.g. tildu) and its replacement string ũ. You enter the u character normally, and then immediately launch the Emoji & Symbol viewer panel. Search for the string combining and then double-click the combining tilde that you find there. That places the tilde over the letter u, press return, and your new replacement is done.

For those applications that support Edit menu > Substitutions > √ Text Replacement, typing the word tildu will either automatically insert the character combination automatically, or prompt with a small dialog showing the symbol, in which any character other than Esc or clicking the x on that dialog will insert the character.

Searching for "u with tilde" gives the following:

- Pie Lover

P.S. I see that others have also pointed out that Character Viewer would be helpful. It's an interesting feature of macOS that I didn't know about.

For accents not in the usual keyboard, activate ABC Extended instead. There Option n will give you 8 characters with tilde above, including ũ.

I can't think of a language that uses this, but you probably have one?

it can be found in "character viewer" in the "latin characters" section.

you can add it to your "favorites" for quick access.

Holding down the "u" key seems to work in my case (see below).

- Pie Lover

P.S. Typing ¨~¨ followed by ¨u¨ does not work

You may have to check a font family to see if such a character is offered.

What keyboard layout (language) are you using?

Some layouts don’t have some combinations. Generally the Extended keyboards have most glyphs.

sorry, but, look closer. your screen grab of the popup doesn't include the "ũ" character, which is the same as the OP's issue.