An upgrade knocked my site offline; how long until it's restored?

Hello and welcome @Scott-CC :slight_smile:

As Linca said, a second rebuild can often give it a kick and resolve some things. :crossed_fingers:

Though as it’s an ‘oops’ page you may also find more detail in your /logs if there’s a conflict somewhere.

Safe mode is also worth trying as well. This can help narrow it down to a plugin or theme component which you can then disable while you work out what the exact issue is.