Hi,
Similar problem when URL contain non-English characters.
The below command works fine in 10.15 (The wikipedia page for "Japan"):
$ open https://ja.wikipedia.org/wiki/日本
which show error in Big Sur like:
$ open https://ja.wikipedia.org/wiki/日本
The file /Users/myMac/https:/ja.wikipedia.org/wiki/日本 does not exist.
I have to encode the URL in Big Sur:
$ open https://ja.wikipedia.org/wiki/%E6%97%A5%E6%9C%AC
I think the escaping part of open command in Big Sur has bug.
Please check about it.