My biggest issue with Nextcloud is there is no LTS version. Employees do NOT like things constantly changing, and Nextcloud has some pretty major changes every 4-6 months. As an admin you really have to keep up to date, or you run into trouble, not just with security, but with trying to upgrade later, as you can’t upgrade across major versions.
In my opinion, a 2-3 year supported LTS version would make Nextcloud way more attractive to hosting in stable environments.