I'm in a position to recommend similar for a large organization, but am on the fence. They have SharePoint on-prem and Office, and are being pulled to Office 3

I'm in a position to recommend similar for a large organization, but am on the fence. They have SharePoint on-prem and Office, and are being pulled to Office 365 by MS sales folk. I'm definitely pushing to linux containers for apps, etc, and part of me wants to recommend Libre. There's a lot not to like about Office and SharePoint, but I've yet to find decent open-source document management software that does all the things SharePoint does. I could recommend they stitch together some things, like some of the low-code projects I've seen here, some calendar apps, some dropbox clone, BI/reporting tools, etc. into a Kubernetes environment. But that's more complex than "go pay N/user/mo for this service". You have to get SSO working for all the things, and each has their own quirks, etc. Any HNers out there have recommendations for open source tools to replace SharePoint/Office 365?