I used Nextcloud to store and share sensitive information like insurance, identity and tax documents. Not a big deal if it was ever down for a while, but I didn’t trust it was hardened enough. Only other thing I was using it for was backups and I switched to S3 for that.
I know what I’m doing and good at following best practice, etc. But at the end of the day I’m just a dude running docker. There’s too much to lose if there was ever a 0-day or I misconfigured something.