I'm hitting this too, and TinCanTech's link actually helped me quite a bit.
OpenVPN client: Community Edition, specifically OpenVPN-2.5.3-I601-arm64.msi
Client OS: Microsoft Windows [Version 10.0.22000.160] (current Insider Preview Dev; yes, ARM64)
OpenVPN server: free tier of vpnbook.com, US1 region
I have confirmed this same config and OpenVPN version works on x64 and ARM64 Windows 10.
I don't have access to the server config, but I don't think that actually matters here since the log file shows a problem very early on.
Here's the client configuration I'm using:
client
dev tun3
proto tcp
remote x.x.x.x 80
remote y.y.y.y 80
resolv-retry infinite
nobind
persist-key
persist-tun
auth-user-pass
comp-lzo
verb 3
cipher AES-128-CBC
fast-io
pull
route-delay 2
redirect-gateway
<ca>
-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----
</ca>
<cert>
-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----
</cert>
<key>
-----BEGIN RSA PRIVATE KEY-----
-----END RSA PRIVATE KEY-----
</key>
When I use this to connect, I get a modal dialog with the text in the name of this thread and this in the log it links to, just like the OP:
2021-08-24 15:15:39 WARNING: Compression for receiving enabled. Compression has been used in the past to break encryption. Sent packets are not compressed unless "allow-compression yes" is also set.
2021-08-24 15:15:39 DEPRECATED OPTION: --cipher set to 'AES-128-CBC' but missing in --data-ciphers (AES-256-GCM:AES-128-GCM). Future OpenVPN version will ignore --cipher for cipher negotiations. Add 'AES-128-CBC' to --data-ciphers or change --cipher 'AES-128-CBC' to --data-ciphers-fallback 'AES-128-CBC' to silence this warning.
2021-08-24 15:15:39 Flag 'def1' added to --redirect-gateway (iservice is in use)
2021-08-24 15:15:39 OpenVPN 2.5.3 Windows-MSVC [SSL (OpenSSL)] [LZO] [LZ4] [PKCS11] [AEAD] built on Jun 17 2021
2021-08-24 15:15:39 Windows version 10.0 (Windows 10 or greater) 64bit
2021-08-24 15:15:39 library versions: OpenSSL 1.1.1k 25 Mar 2021, LZO 2.10
2021-08-24 15:15:39 ERROR: Failed retrieving username or password
2021-08-24 15:15:39 Exiting due to fatal error
Searching for "Failed retrieving username or password" and "arm64 openvpn", I found this issue which is what I am hitting:
https://community.openvpn.net/openvpn/ticket/1418
There's a fix coming soon:
https://patchwork.openvpn.net/patch/1871/
If your system isn't ARM64 and you're not on a Windows Insider Program version of Windows, then this likely doesn't apply to you. :/