It seems that pre-2015, the world and his mother wanted to get Bootcamp to boot to Windows just once, and keep the default startup disk as Mac. There are loads of threads that say to use Bless or Bootchamp: https://superuser.com/questions/36266/boot-camp-is-it-possible-to-restart-directly-to-windows-from-mac-os-x/167577#167577, how to quickly reboot from OSX to Windows and back.
But, these methods no longer work, it would seem.
I found this Reddit post which says to use
sudo systemsetup -setstartupdisk /Volumes/.BOOTCAMP/WINDOWS && reboot, but I don't think this sets it to boot next time only; and all the advice I've read says not to test out sudo commands without fully understanding them, which I certainly do not.
So could anyone tell me, or point me towards some information that would get this to work for Catalina. I'm either looking for a modern version of Bootchamp (though, I'm sure Googling it would have got me to it if something like that existed), or a new way to run
sudo bless -mount "/Volumes/BOOTCAMP" -legacy -setBoot -nextonly;sudo shutdown -r now.
I know I'm lazy and holding down the option key when I need to boot to Windows really isn't all that problematic, but I think I may have a faulty option key, as sometimes it boots to mac a few times before finally working. It would be so much easier if it could be done with something like the command above.