Steps to reproduce:

1. Configure repo https://repo.zabbix.com/zabbix/6.4/ubuntu/dists/focal/
2. apt install zabbix-agent2 zabbix-sender
3. zabbix_sender -c /etc/zabbix/zabbix_agent2.conf -k key -o value

Result:
zabbix_sender [1922324]: ./zabbix_agent2.d/plugins.d: [2] No such file or directory
Expected:
No errors

This error is caused by the packaged config including the following line:

Include=./zabbix_agent2.d/plugins.d/*.conf

Which should instead be this, to match the other includes:

Include=/etc/zabbix/zabbix_agent2.d/plugins.d/*.conf