Got fed up trying to work out which .ssh key maps to which host hence: alias (or function) lskeys

.bash_aliases

alias lskeys='for kf in ~/.ssh/*.priv; do read -rst 2 size fingerprint userid txt <<<$(ssh-keygen -l -f ${kf});\
  printf "KEYFILE: %-50s - BITS: %-6d FP: %s, USER: '%s', INFO: '%s'\n" "$(basename ${kf})" "${size}" "${fingerprint}" "${userid}" "${txt}"; done'

  
  

lskeys.bashsrc

#!/bin/bash

#File: lskeys.bashsrc

# usage:
#  source <path_to>/lskeys.bashsrc
#  lskeys

# See the 'simpler' version done as a bash alias

# Note this assumes you name all your private keys <whatever>.priv
# as per the GLOB variable
# This works as I use <user>@<domain>.<fqn>.<pub|priv> for my key files
# You may be able to use the 'file' command as this seems to be
# able to tell what a private key file looks like, but for me not all formats.
# You can try that by setting USE_EXT to false.

USE_EXT=true

if ${USE_EXT}; then
  GLOB=~/.ssh/*.priv
else
  GLOB=~/.ssh/*
fi

function ispriv () {
  ${USE_EXT} && return 0
  # b = brief
  # L = Force dereference (or symlinks report just that)
  file -bL $1 | grep -q "private key"
  return $?
}

function lskeys () {
  for kf in ${GLOB}; do
    ispriv ${kf} || continue
    read -rst 2 size fingerprint userid txt <<< "$(ssh-keygen -l -f ${kf})"
    if [ "${userid}" == 'no' ] && [[ "${txt}" =~ comment ]]; then
      # Handle where there is no userid in the private key
      txt="${userid} ${txt}"
      userid="<none>"
    fi
    printf "KEYFILE: %-50s - BITS: %6d, FP: %s,  USER: '%s', INFO: '%s'\n"\
      "$(basename ${kf})" "${size}" "${fingerprint}" "${userid}" "${txt}"
  done
}

Two versions:
A simple one as a bash alias and a more complicated one as a sourcable bash script, which deals with edge cases and is more adaptable.

I suggest using ssh-keygen like this:

cd .ssh
ssh-keygen -t ed25519 -f username@target.system.domain -C "Comment string, e.g. local_user@local.domain"
mv username@target.system.domain username@target.system.domain.priv