In the most recent editions of carpet, when players spawn using /player spawn and /player shadow, they are consistently shown as 'Anonymous Player' in the server list.

Before, these players would be listed with their respective usernames. I have been unable to locate any documentation regarding this alteration or the reason behind it.

It's likely related to the new recent Allow Server Listings option, it's likely fake players not being real ones default to disabled, or it was set to that when whatever method that now takes it was updated.

I don't think it's bad though, imo it makes sense for fake players to not show up there, especially when people spawn bots that aren't actually players on the server and it could cause confusion.

it could cause confusion.

Definitely agree, and it is reasonable to remain default behaviour.

It would also be good to have the option to set it back to previous behaviour, especially for external monitoring.