is there an installation guide to have a direct alternative with Nextcloud from a SaaS service as Microsoft 365?
Something with at least a centralized identity solution, a mail server and nextcloud that use that and that is completely functional, based on a VM or docker image.
This way migrating from a SaaS offering would be much much easier and user count would go way up.
Check out the Ansible configuration.
It will require you have technical know-how, otherwise you can pay a hosted provider to run it for you.
Easy is subjective. Depends on how well you can configure it as an admin. There are a ton of variations, which will depend on your particular setup. Google or search the forum for tons of examples.
You’ll need a number of virtual machines or containers, hence needing to understand ansible or some other method for taming the whole process. You could try the new All in One Docker container.