invalid format err for ed25519 key, need to add a newline at the end of the key make to win ssh work with it

Prerequisites

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

Steps to reproduce

PS C:\Users\jy> C:\Users\jy\scoop\apps\openssh\current\ssh -V
OpenSSH_for_Windows_9.5p1, LibreSSL 3.8.2

PS C:\Users\jy> C:\Users\jy\scoop\apps\openssh\current\ssh -i ./gcp-ed25519 abc@35.xxx.yyy.140
Load key "./gcp-ed25519": invalid format
abc@35.xxx.yyy.140: Permission denied (publickey).

I can connect to server with this key file in wsl ssh and xshell 7, but not windows ssh

add a newline at the end of the key make win ssh accept this file, but why? (see also: https://stackoverflow.com/a/68593742)

Expected behavior

connect success

Actual behavior

PS C:\Users\jy> C:\Users\jy\scoop\apps\openssh\current\ssh  -i ./gcp-ed25519 abc@35.xxx.yyy.140
Load key "./gcp-ed25519": invalid format
abc@35.xxx.yyy.140: Permission denied (publickey).

Error details

None

Environment data

PS C:\Users\jy> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.4.2
PSEdition                      Core
GitCommitId                    7.4.2
OS                             Microsoft Windows 10.0.19041
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Version

9.5

Visuals

No response

Start by reproducing the Windows OpenSSH 9.5 command with the ./gcp-ed25519 key, comparing the file with and without a final newline. Investigate why Windows ssh rejects the otherwise usable key and confirm the expected behavior against WSL ssh and Xshell. Done means the key is accepted by Windows ssh without manual newline editing, with the behavior covered by an appropriate project test.