I haven't even used Libre Office in I'm guessing a couple of years. Even then, it was just to print out some invoices, but I don't even do that anymore.
I don't guess that has anything to do with anything, but I do really like KMail and Thunderbird. I use Thunderbird on my work laptop and KMail on my home workstation. I prefer KMail because it is so powerful, and well, I seem to prefer anything KDE does.
I suppose KMail would be the most integrated and comparable to Outlook if you also use Kontact. That's what I have been doing for a long time now. It is pretty cool how they work together.
If you use a groupware like Kolab or NextCloud, you can expand all of these features to be able to collaborate with a team. All free and open source.
We live in amazing times!
So when I first forayed into Linux and OpenSource I was a KDE user. Back then KDE was very German, sparce, and pretty close in resemblance to Windows 95 and Office 97. Bwahahaha
I resisted the pull of that sexy Gnome for as long as possible but finally succumbed to that "Ooh look, shiny!"
Over the years I've tried all the DE's. :-)
Oddly, I prefer OpenBox and KDE, lol. Polar opposites. KDE went through some funk there for a while, but I'm really liking the newest stuff. Needs a reasonably hefty machine though.
See now OpenBox is great for having less bloat I just hated faffing around with configuration all the time to get things to work although that may have changed now?
I don't think it has changed in that regard, but there is always LXDE, which is OpenBox without the need to configure everything (I think).