The above Syncshells are public, temporary Syncshells.
This means that everyone is welcome to join, to share their character visuals/mods with other players on the Crystal Data Center. (Most likely on Balmung)
The listed Syncshells are automatically changed out on a monthly basis, to ensure they do not fill up with inactive characters.
Understand that these Syncshells are unmoderated, and adult/NSFW content is allowed.
If you encounter things upset or bother you, you are encouraged to use Mare's in-built functionality to pause the Syncshell.
These Syncshells naturally require the Mare Lamentorum and Penumbra plugins in FFXIV/Final Fantasy XIV.
If you need help with these, see the guide linked below: