ssh-add gives invalid format error

[gh-test-01-king]

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest version
• Search the existing issues.

Steps to reproduce

> ssh -V
OpenSSH_for_Windows_8.1p1, LibreSSL 3.0.2
> ssh-keygen -t ed25519 -C email@example.com -f id_email_example_com
...
> ssh-add id_email_example_com

Expected behavior

key being added

Actual behavior

Error message `Could not add identity ".\id_email_example_com": invalid format`

Error details

No response

Environment data

Name                           Value
----                           -----
PSVersion                      7.4.5
PSEdition                      Core
GitCommitId                    7.4.5
OS                             Microsoft Windows 10.0.19045
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Version

OpenSSH_for_Windows_8.1p1, LibreSSL 3.0.2

Visuals

No response