Dead keys doesn't work with text processors in Ubuntu 20.4

Since a time ago I'm experimenting problems with dead keys in text processors like LibreOffice Writer, also with FeatherPad, in Telegram desktop official tool, but not in navigators like Google Chrome or Firefox. I use a lot the accent mark for spanish writing. I have Lubuntu distribution installed:

Operating System: Ubuntu 20.04.2 LTS Kernel: Linux 5.4.0-71-generic.

Any help will be very appreciated.