On 129.3-rc, I tested pressing ⌘+T when a YouTube video was in full screen and this correctly resulted in Orion opening a new tab, and switching focus to it. The bug appears to still occur on -beta so this is yet another issue that can be added to the massiveNext Release list @Vlad
I also tested both versions of When opening a link in a new tab, make it active and focus was switched to the new tab in both cases, as users would expect.