correct way to use variables in ansible inventory

Question

So I started learning ansible curiously and the instructor told me to experiment some variables in inventory and I tried with my little knowledge

this is my inventory file

[newserver]
server1 ansible_host=54.208.201.158
server2 ansible_host=3.80.57.225
[newserver:vars]
ansible_user=ec2-user
ansible_ssh_private_key_file=/home/ec2-user/pem/safety.pem

and this is my playbook file reprctce.yml

---
- name: install nginx ( play name )
  hosts: newserver
  become: yes
  tasks:
   - name: install nginx ( task name )
     yum:
       name: nginx
       state: latest
   - name: install node ( task name )
     yum:
       name: nodejs
       state: latest
   - name: starting nginx (task name)
     service:
       name: nginx
       state: started 

when I started running these playbooks with ansible navigator it throws error as

fatal: [server1]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: no such identity: /home/ec2-user/pem/safety.pem: No such file or directory\r\[email protected]: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).", "unreachable": true}

fatal: [server2]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: no such identity: /home/ec2-user/pem/safety.pem: No such file or directory\r\[email protected]: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).", "unreachable": true}

but the fact is I double checked my ssh key file and it was absolutely correct.

I also tried with old fashioned ansible-playbook run command and the result is it actually made changes in second server and displays first server as a unreachable one and at this point I have really confused My guess is I could have done error in constructing inventory file , help me to find my error