For an office suite, Calligra is a nice additional one to have alongside LibreOffice. Cons: Probably a smaller feature set compared to LibreOffice, and I'm not sure about compatibility with MS Office. Pros: is faster, more reliable, and IMO looks better than LibreOffice too.
Btw, regarding Flatpak, I've had multiple issues related to mouse cursor, fonts, and local folder access - all related to the sandboxing of apps, all resolvable, but potentially a problem for a non-technical user. I've had much better experiences with AppImages, but I don't know if they have a graphical app store like interface; even the AppImageUpdate idea is still catching on.
Haven't really used any of them...so just throwing out the options without being able to tell if they are any good.
There are several closed-source suites, but on the non-LibreOffice open-source side you have Calligra Suite, Abiword, Gnumeric, and OnlyOffice Desktop.