I have been looking.at the same thing. Basically alternatives to Google Workplace or MSFT 365.

lemmy.ml/post/21772726. I think most people are using a hosting providers email and web hosting and then maybe running Nextcloud and other apps themselves though there are some providers who are doing integrated email and Nextcloud.

There are things like coop.cloud and yunohost that appear to be trying to provide.out of the box self hosting ‘recipies’ Im just starting to look at yunohost but just for me / the family. - Id personally love to meet people and work through using these together as I am not an expert. It would seem that these might be the ‘killer app’ for self hosted alternative cloud services but Im not sure and they might not be quite mature enough. I have know knowledge of the admin overhead.

Google and MSFTs free for non-profits mean that clubs/small charities end up using those two anyway.