I searched this community and couldn’t find anything about odt, I found a few odt viewers on F-Droid and Aurora when I searched ‘odt’, but the only editors for odt, were ironically the proprietary Google Documents and Microsoft Word.
Have you found anything else?
May I ask why? Using alternative sources from the vendors themselves usually isn’t any less secure than using the official F-Droid repos. It’s a common thing on Linux.
Has Collabora made its packages reproducible, so independent people can check if their package is built from the source code without modification?
Well it seems they don’t publish a signing key, so that’s a good reason against it.