Hey. Recently Telegram team contacted me about Ghost Mode.
As clarified, the only possible way to open chats in ghost mode is to do it same as in official apps - popup them like you long-tap it.

For now, Ghost mode in Nicegram is remotely disabled.
Feature will return in a bit different way with a bit different name too.

Stay tuned and keep an eye on this channel and @nicegramdev updates.

P.S. It was expected, so that's why I have a remote toggle for that.