thank you very much for your reply, I have used
/usr/bin/nice -n 5 /usr/bin/php7.3 -q
and
/usr/bin/nice -n 5 /usr/bin/php -q < this one to make sure always work since it is symlinked to the current php version
but both settings fail, I still receive php5 cronjob messages, any idea what can be wrong?