Ah, yeah, sorry for the misunderstanding. I’m actually not 100% sure what PureOS is doing there. GNOME used to use that tray, but starting with GNOME 3.26, it has been removed.
Various GNOME shell extensions (like TopIcons Plus move those icons from that tray to the top bar (which I think is nicer, as even though that tray was just a small sliver when closed, that small sliver still got in the way and was annoying in my opinion).
Interestingly, my version of PureOS appears to be running GMOME Shell 3.22, yet icons still show up in the top bar. But I don’t explicitly see a shell extension installed that would do that. So Pursim must have done some tweaking to move the icons to the top bar (for me, it was the top right, near the Wifi/Ethernet symbol, but TopIcons Plus puts them at the center, near the time)