Which UARTs are usable?

I’m trying to figure out which UARTs are available to use. On the LS header, UART1 works fine, but UART0 seems to be a no-go. It’s commented out in the device tree of the build I’m using (Debian 423) and when I try to enable it with dbootimg and dtbtool, the board fails to boot (similar reports in this forum of boot failures around this UART).

Other UARTs are advertised on the secondary HS header, but with the note “Currently not configured in SW”. Does this mean I could add them in the device tree, or that they’re completely inaccessible to me? If the latter, what are my options for enabling UARTs other than UART1, which ideally I’d like to keep free for the debug console? Any guidance here would be much appreciated.