With most apps on my macos (TextEdit, TextWrangler, Skype, WeChat, Mail, Xcode, Android Studio, Chrome, Firefox, Safari, etc.) when I hold down a letter like E, I get the choice of accents to use from the PressAndHold popup:
Alas, when I switch to a powerful document editor like LibreOffice, I lose this ability to choose accents.
Note: Sierra and High Sierra
Best Answer
This feature is not supported by LibreOffice 5.3 according to this page. It's the same for 5.4 according to my tests. I did not try the dev version 6.0.