There is few of things for you to check.
1. Check your Github PAT. Check the permission scopes and expiration date of token you are currently using. You might need to generate new one. For the details documentation related to it you can check it here.
2. Then delete old github credential from Credential Manager on your computer by searching it and remove git:https://github.com

Additional to check :
- Check Repository Permission and ensure that if you still have write access on it, because if you only have read access it will never work.
- Check the SSO Authorization, if it using SSO then you might need to authorize the token on it.