https://www.zabbix.com/documentation/current/en/manual/installation/upgrade/packages/rhel#update-repository-configuration-package

The upgrade notes for 7.2 state the URL for RH8 to be:
rpm -Uvh https://repo.zabbix.com/zabbix/7.2/release/rhel/8/x86_64/zabbix-release-latest.el8.noarch.rpm

x86_64 folder does not exist, should be:
rpm -Uvh https://repo.zabbix.com/zabbix/7.2/release/rhel/8/noarch/zabbix-release-latest.el8.noarch.rpm