Hi!

I'm running Gentoo and that bug happens in Plasma 5.18.5 and 5.19.1.

Plasma's behavior is erratic. I've set the US INTL WITH DEAD KEYS layout, which is the only one I should use, but it doesn't apply correctly to all applications.
For example in Konsole the dead keys doesn't work at all and I can't even write " ". I've found that configuring the layout per application in KDE Settings and changing it to US is a workaround - that way I can at least type " ", but couldn't easily write a portuguese text in vim (á é ç ã, etc). That's really anoying.

LibreOffice only works if it's started from the command line - I've checked the command that plasma menu's runs and it's the same: libreoffice --writer.
So it appears to me is a Plasma bug.

So, I finally tryed:
setxkbmap -layout us -variant intl

And done. Works perfectly.