I've used nextcloud for a while now, but it does suffer from jack of all trades syndrome. I've started offloading the things I use it for to other services that do a particular thing better. Syncthing for general file syncing across my devices, Immich for managing photos, Radicale for contacts and calendar sync...
If you're just looking for an all in one Google Drive like experience for your files though, Nextcloud is as good as it gets.
To be fair... Flakes are still marked as an experimental feature, so they are telling you it probably won't be documented and the interface could change. But yes, given how widely adopted they are in the community, it's definitely time to document them better and ideally make it the default for new setups.