ubuntu20.04 how to convert ISO image in physical server?

is there any straight procedure for bare metal server convert to OS image to push rest of the bare metal serves

You were not specific in your question, what exactly do you want to do. I assume your goal is to "clone" your existing server installation to other machines, including all the configuration and customizations you have made. This is possible, however there is no simple way to do that.

In any case, you will need the possibility to boot your server from an external medium - Ubuntu live DVD or USB - and not from your installed system. In other words, you need physical access to your server.

After you boot from a live image, you have two options:

1. if the servers you want to clone your installation to have the same size disks as your source server, the simplest option is to copy your disk image to an external disk as a file (using dd), and then on target servers write back contents of that file to the (raw) server's disk. With this method you copy all partitions at once and the partition table itself, but it needs to be repeated for each physical disk.
2. if the target servers have different size disks, mount each filesystem (partition) and archive its contents to a .tar file on an external disk. On target servers, you need to partition the disk according to your needs and format the partitions, then untar the .tar files to appropriate partitions after mounting them.

In both cases, you need additional adjustments before you can boot the copied system. You may need to adjust /etc/fstab file if you used UUIDs there (which is default for Ubuntu) and not device names - you can avoid this if you change your original /etc/fstab to use device names before cloning the system. You may need to change the network configuration, if you use static IP addressing and not DHCP. In case of method 2), you also need to install GRUB on your boot device.

I am not going into details here as they may change according to your case. I have successfully "cloned" several servers and desktops using this method, but it is by no means straightforward. But in some cases, it is still less work than repeating all changes and customizations that have been done over several years to a running server.

Yes, that's called "Installing Ubuntu".

There are numerous articles on this site, and elsewhere on the internet, describing how to "burn" the ISO to a USB or DVD and running the installer.

If your server has "remote management processor", you can probably also remote mount the ISO directly there. Please read your server manual to see if this is a possibility, and how to do it.