Great video!!!
Now I see the issue with the extra colon, but I do not get the error - probably because I tested with an S3 backend (instead of GCS).
Seems like the web GUI always adds ":/" to the end of the path if the path doesn't already contain ":/", no matter which remote you are using. This is a bug and can get quite interesting if you try hitting backspace to delete the "/" and then hit enter - I easily managed to make this (local) remote:
myRemote:::::/
The natural next step would therefore be to create a GitHub issue here:
There is just one major problem: The rclone web GUI project seems to be abandoned, the last update was in July 2021:
Source: GitHub - rclone/rclone-webui-react: A full fledged UI for the rclone cloud sync tool (2023-04-15)
So I guess you will have to manually work around the problem, or see if you can find a better maintained alternative. I quickly tried but had no luck, sorry.