By default if you create a private key for SSH, it will create something like .ssh/id_rsa
Linux will always search for and offer this key when connecting to servers.
If you put extra keys in your .ssh directory like id_rsa_realtechtalk.com, they will be ignored by default and NOT used or offered (you can verify this with ssh -v) and see it is not being offered.
Here is how you add the extra SSH keys so they are all offered:
#this gives........