I am looking at it - I just realized there is more than I expected - I will have to check how my system reacts.
FOLLOWUP:
There will be applications which requires qt5 - among those are vlc - which can be removed - but consequences are unknown - I did remove vlc ignoring the dependency
sudo pacman -Rdd vlc
and manjaro-settings-manager
sudo pacman -Rns $(pacman -Qsq manjaro-settings-manager)
After that I removed the excess packages - hopefully not crippling it - I have yet to find out if I did 
.
The result is the packages to keep
a52dec
db5.3
krb5
libdbusmenu-qt5
libde265
plasma5support
python-html5lib
qca-qt5
qt5-base
qt5-declarative
qt5-graphicaleffects
qt5-multimedia
qt5-quickcontrols
qt5-quickcontrols2
qt5-speech
qt5-svg
qt5-tools
qt5-translations
qt5-wayland
qt5-x11extras
qt6-5compat
x265
To deduce what the consequeses are I suggest run create a list and then feed the list to pacman remove command using the --print argument as this will do nothing but print what would have been done.
pacman -Qqn | grep -e '5' > pkg5-list.txt
Then edit the file, and remove the packages from the above output showing the packages to be kept, save the file and feed the result to pacman
sudo pacman -Rns --print - < pkg5-list.txt
Then deduce whether you are ready to remove the --print and execute the command for real