Comparing the termcap between Bookworm and Trixie reveals no differences,
so this is not a termcap issue.
Digging into VIM docs, there appears to be a setting "belloff". If I set
belloff=cursor, then the annoying behaviour goes away.
The VIM documentation states for this:
'belloff' 'bo' string (default "")
global
Specifies for which events the bell will not be rung. It is a
comma
separated list of items. For each item that is present, the bell
will be silenced. This is most useful to specify specific events
in
insert mode to be silenced.
...
cursor Fail to move around using the cursor keys or
<PageUp>/<PageDown> in |Insert-mode|.
The thing is, VIM is not failing to move around when using PageUp /
PageDown while in insert mode, but it still rings the bell unless belloff
is set to "cursor" - so Trxie's VIM behaviour and the VIM documentation
disagree.
Seems to me to be a clear cut VIM bug.