Issue, let say, "SOLVED" - I ma using the latest available firmware for iDRAC (6.10.30.20) and there is no option "Plug-in Type" so just for my curiosity I have downgraded iDRAC to older version (5.10.10.00) and after this I was able to change "Plug-in Type" to HTML5 what solved the NO SIGNAL issue - so seems problem is with 6.10.xx.xx iDRAC firmware.
I am not able to install Linux distributions on the Dell PowerEdge C6525 servers, I was trying to install RedHat Enterprise Linux 7.9, 8.0, 8.6, CentOS 7.9 and Ubuntu 22.04 - after starting ISO image (mounted as virtual CD or connected via NFS share) the KVM (from iDRAC) displays "NO SIGNAL" information after boot options screen while Gentoo distribution (Live ISO image) and VMware ESXi is working fine. Please note that there is one extra hardware added to these servers - it is network card Mellanox ConnectX-6 Dx Dual Port 100 GbE QSFP56 Adapter. The BIOS and iDRAC is updated to the latest available versions (iDARC - 6.10.30.20, BIOS - 2.10.2) but this doesn't help here. Any clue what is going on on these types of servers?
Linux installation issue on the PowerEdge C6525 servers - NO SIGNAL on KVM