There is no trick here
Sorry I missed you are on centos 8
yum remove spamassassin
then remove smtp inet n - n - - smtpd -o content_filter=spamassassin from /etc/postfix/master.cf
Remove the following code which is at the end of the file:
spamassassin unix - n n - - pipe flags=R user=spamd argv=/usr/bin/spamc -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}
Also delete these lines Any way to disable spamassasin? - #2 by usmannasir1
Finally, restart Postfix:
service postfix restart