See this GIF:

When pop-up links are clicked, the start page is replaced, but an extra tab space is created. It remains empty until a new tab is created. I'm pretty sure I have observed this in a few places, but Google Classroom was the one I happened to open when I decided to report this.
The empty space should be removed as the new tab is removed.
Orion 1.0.3 (142), WebKit 624.1.2.19.2, Mac 26.3 (Build 25D5087f)
Tahoe (26)