That's a core bug, and your forum is fine. Only the System Info page is affected.
Your host has exec() in PHP's disable_functions. Flarum's info command calls exec() without checking whether it's available, so the call fatals and the page gets nothing back. The giveaway is the namespace in the error: PHP prints Flarum\Foundation\Console\exec() when it can't find a global function, and a disabled function is removed from the function table entirely, so that's exactly what a blocked exec looks like.
You can confirm it in a phpinfo page, or by asking your host: look for exec in the disable_functions list.
Nothing to fix on your side. The forum, the admin panel and everything else work normally; it's just this one page that can't build its report. It needs a function_exists('exec') guard in core, which I'll report upstream.
For what it's worth, this isn't new in 2.x. 1.8.19 has the same unguarded call in the same function, so if your 1.x forum's page loads, that server is allowing exec.
