I don't see SSMenuAgent in System Settings > Menu Bar at all (not in Controls or in the Allow section) on two Macs running 26.3 (one updated from 26.2, the other directly to 26.3 from Sequoia), so I do not believe that it 'came with 26.3'.
Is it in the Controls section, or the Allow in the Menu Bar section? The latter does seem to have some issues, for example early on in macOS 26 a package tracking app that I use had two entries there, one for an older version of the app, there's only one now so that resolved itself. With 26.3 in that section on one Mac (the one updated from 26.2), I see an entry for iStat Menus and another for iStat Menus Menubar and toggling the first one does nothing; on the other Mac, there is only the iStat Menus Menubar option.
Toggling the menu bar item on should not give permission, that is controlled in System Settings > Privacy & Security > Screen & System Audio Recording. I say should not because I see only 3rd party apps listed there, and SSMenuAgent is an Apple app.
If it's showing up in the Allow in the Menu Bar section (which is dynamic based on apps that have requested it), I suspect that etresoft's suggestion that it's a remnant is correct, and in that case I'd just leave it off and it will probably disappear at some point.