What does the red 1! msg mean in the Byobu status panel?
Byobu checks for updates on macOS using this script:

# Mac OSX
# check if any new versions have been installed since
# we last cached. this may not recognize formulae
# installed with HEAD
for f in $(brew --prefix)/Cellar/*; do
    [ "$f" -nt "$mycache" ] &amp;&amp; return 0
done
# nothing new has been installed, so check wether the
# formulae database was updated
[ "$(brew --prefix)/Library/Formula" -nt "$mycache" ]