This worked for me. YMMV.
wget https://dl.fedoraproject.org/pub/fedora/linux/development/34/Everything/source/tree/Packages/s/spamassassin-3.4.4-8.fc34.src.rpm yum install rpm-build openssl-devel gcc make perl-Geo-IP perl-Mail-SPF perl-Net-CIDR-Lite yum update perl yum install perl-Test-Simple perl-generators perl-Digest-SHA1 perl-Test-Simple perl-BSD-Resource rpmbuild --rebuild spamassassin-3.4.4-8.fc34.src.rpm rpm -Uvh /root/rpmbuild/RPMS/x86_64/spamassassin-3.4.4-8.el7.x86_64.rpm systemctl restart spamassassin
Seems to work, and recognized by Webmin.
I have no idea whether the Web GUI will properly interact with the new installation because I never use it anyway. Spamassassin is one of those things that I’m in the habit of doing from the shell. But it does at least recognize it.