In the docs at https://docs.microsoft.com/en-us/visualstudio/ide/finding-and-replacing-text?view=vs-2019#multi-caret-selection it says:
Ctrl+Shift+Alt+, Add all matching text as selections
That doesn't work (_Version 16.7.0 Preview 3.1_) but Alt+Shift+; does. (_Googled it_)
@JeepNL Thanks for letting us know; we'll check in to this and report back soon.
There's a PR on the public repo (https://github.com/MicrosoftDocs/visualstudio-docs/pull/5978) that'll address this; it should be published, soon.
@JeepNL We've updated the keyboard shortcuts in the Multi-caret selection section on the "Find & Replace Text" page to reflect what you reported. We'll make further updates to the page to capture recent feature changes, soon. Meanwhile, we thank you for your help with improving our documentation!