Hi @spendiff,
Provided the IP detection in Wordfence > All Options > General Wordfence Options > How does Wordfence get IPs correctly detects individual user IPs, then any blocking towards unauthorised access to this username will only block the IP address from your site. You can check this by seeing if your own public IP as seen on https://whatsmyip.com also displays under Detected IP(s) in this section.
Also ensure that Wordfence > All Options > Brute Force Protection > Immediately block the IP of users who try to sign in as these usernames does NOT contain this username as this would block everybody attempting to sign in without exception.
You could also mitigate causing lengthy problems with legitimate login attempts that have failed by setting Wordfence > All Options > Rate Limiting > How long is an IP address blocked when it breaks a rule to a shorter timeframe such as 5 minutes. However, if you start to notice an unacceptable amount of traffic hitting your site, you may need to lengthen this time again.
I hope that helps you out!
Thanks,
Peter.