Please help with `No solution found within the allotted time. Try harder?' warning message

[Rodolfo Medina <rodolfo.medina@gmail.com>]

Wishing to do a full-upgrade from bookworm to trixie, the commands

 # aptitude update
 # aptitude install dpgk aptitude apt
 # aptitude full-upgrade

which had always worked in the past, gets a `No solution found within the
allotted time.  Try harder?' warning message.  Please help.

Thanks for any help.

Rodolfo