Weird! https://support.apple.com/en-us/HT201236 lists them under "document shortcuts." Well, not c-u although I swear that one worked too. Maybe they removed them and this document is out of date? I haven't used a mac in a long time, so it's possible. Damn shame if they did, I always liked that feature.

[edit] A friend checked on his Montery machine and said they work as expected in system text boxes.