example of how to use host alias to separate keys for same host but different sub route. taken from: https://docs.microsoft.com/en-us/azure/devops/repos/git/use-ssh-keys-to-authenticate?view=azure-devops&tabs=current-page#q-i-have-multiple-ssh-keys--how-do-i-use-different-ssh-keys-for-different-ssh-servers-or-repos

ssh-config.sh

# The settings in each Host section are applied to any Git SSH remote URL with a matching hostname.
# Generally:
# * SSH uses the first matching line for each parameter name, e.g. if there's multiple values for a
#   parameter across multiple matching Host sections
# * "IdentitiesOnly yes" prevents keys cached in ssh-agent from being tried before the IdentityFile
#   values we explicitly set.
# * On Windows, ~/.ssh/your_private_key maps to %USERPROFILE%\.ssh\your_private_key, e.g.
#   C:\Users\<username>\.ssh\your_private_key.

# To use the same key across all hosted Azure DevOps organizations, where the SSH URL host is
# ssh.dev.azure.com (like [email protected]:v3/some_organization/some_project/some_repo), add
# the Host section below:
Host ssh.dev.azure.com
IdentityFile ~/.ssh/your_private_key
IdentitiesOnly yes

# Since all hosted Azure DevOps URLs have the same hostname (ssh.dev.azure.com), if you need
# different keys for different organizations (or just different repos within the same organization),
# you'll need to use host aliases to create separate Host sections.
#
# Imagine that we have the following two SSH URLs:
# * [email protected]:v3/org1/org1_project/org1_repo
#   * For this, we want to use key1, so we'll use devops_key1 as the Host alias.
# * [email protected]:v3/org2/org2_project/org2_repo
#   * For this, we want to use key2, so we'll use devops_key2 as the Host alias.
#
# You'll need to substitute ssh.dev.azure.com with the Host alias in the SSH URL you use with Git.
# The SSH URLs above become:
# * git@devops_key1:v3/org1/org1_project/org1_repo
# * git@devops_key2:v3/org2/org2_project/org2_repo
#
# To set explicit keys for the two host aliases and to tell SSH to use the correct actual hostname,
# add the next two Host sections:
Host devops_key1
HostName ssh.dev.azure.com
IdentityFile ~/.ssh/private_key_for_org1
IdentitiesOnly yes
Host devops_key2
HostName ssh.dev.azure.com
IdentityFile ~/.ssh/private_key_for_org2
IdentitiesOnly yes