Ok it worked
I duplicated the php file php7 from the folder /opt/plesk/php/7.4/bin/php in folder
I renamed it as php7.4 and moved it to /usr/bin/
My cron is finally :
/usr/bin/php7.4 /var/www/vhosts/mywebsite.xyz/httpdocs/matomo/console core:archive --url=https://mywebsite.xyz/matomo/ > /dev/null
Thanks for your support.
Philippe.