Thanks for your report. But no, I cannot confirm your findings.

Or actually, you are rights with your specific way. But the winscp:1.2.3.4 is not an URL. URL is like winscp://1.2.3.4.

Hi,
I just had time to test the integration with KeePass (version 2.34).
Following your documentation on https://winscp.net/eng/docs/integration_keepass I was not able to start WinSCP from KeePass.
After many tests I found a working solution. I'd appreciate if someone else could verify my findings and we finally could update the documentation.

orig URL Override:
cmd://"{ENV_PROGRAMFILES_X86}\WinSCP\WinSCP.exe" {BASE:SCM}://{USERNAME}:{PASSWORD}@{BASE:HOST}:{T-REPLACE-RX:/{BASE:PORT}/-1//}
my URL Override:
cmd://"{ENV_PROGRAMFILES_X86}\WinSCP\WinSCP.exe" sftp://{USERNAME}:{PASSWORD}@{BASE:RMVSCM}:{T-REPLACE-RX:/{BASE:PORT}/^$/-1/}

My changes:
URL: WinSCP:1.2.3.4
For personal reasons I fixed the protocol to sftp instead of using the placeholder {BASE:SCM}.
The host/IP address was empty until I replaced the placeholder {BASE:HOST} by placeholder {BASE:RMVSCM}.
Also the port was empty until I changed the last portion of the regular expression from /-1// to /^$/-1/

Kind regards, Willy