In dark mode, all signposts appear in black on black background – so the text is always invisible and the signpost itself often is also invisible.
Dorico 22.214.171.1246. Windows 10.
By the way (change of subject), it is annoying that signposts appear on top of music items. I believe this wouldn’t be so bad if signposts were placed behind them. I mean, on the z axis. Today signposts appear on top of the music and worse, signposts have a background, so they can obscure a lot of the music.