Mastodon used to have a feature that gave instance admins the ability to view direct messages of all instance users directly in the #admin ui. This was part of mastodon's ongoing proactive stance on moderation and harassment. The feature was removed, but now there is a discussion to reintroduce this functionality: https://github.com/tootsuite/mastodon/issues/7304
This would be despite the current possibility for admins/mods to see DMs that have been reported. I'm personally not a fan of this development.