There's [lots of options](https://nextcloud.com/partners/) for using Nextcloud as a managed service.

Yes it is, but you have to pay for it https://nextcloud.com/trial/

It sounds pretty hostile to end users:

Please do not email us from private mail addresses like gmail, gmx and the like. We only provide a trial to businesses > 50 employees. As a small business or private user, we recommend you simply try our demo or talk to one of our partners.

There are managed hosts serving NextCloud though