Update Project (Ctrl+T) - a confirmation dialog ?

There is such a dialog: Settings -> Version Control -> General Settings -> Display options dialog... -> Update. Maybe it isn't available for all VCSs? At least it is for CVS and SVN.

I thought it may be a good idea to provide an optional (that can be turned on and off) confirmation dialog for "Version Control => Update Project" (CtrlT) command. In unstable environments (they still exist, no matter what) where build is broken many times a day - an occasional and unintended update (I happen to type CtrlT instead of Ctrl+Y by mistake quite a lot) may be very disastrous.

May be for those cases a confirmation dialog "Do you really want to update your project ?" could be provided (with an option "Don't ask me again", of course)

Ahhh, this one, right :)

I've disabled it right away first time I saw it. Well, it kind-of works as "Are you sure ?" and is enabled by default. So it's the same as I thought.

That already exists! You must have already ticked the "Do not show this dialog
in the future" option :)

Re-enable it via Project Settings -> Version Control -> General Settings
-> Display options when Update is invoked.

I thought it may be a good idea to provide an optional (that can be
turned on and off) confirmation dialog for "Version Control => Update
Project" (Ctrl+T) command. In unstable environments (they still exist,
no matter what) where build is broken many times a day - an occasional
and unintended update (I happen to type CtrlT instead of CtrlY by
mistake quite a lot) may be very disastrous.

May be for those cases a confirmation dialog "Do you really want to
update your project ?" could be provided (with an option "Don't ask me
again", of course)

Exactly :)

I did it so long ago so that forgot about the dialog completely ...

you can now control this in the version 2021.1.