So indeed rclone doesn't support socks5 yet? I have seem many contradicting information on this, e.g. someone first says socks5 isn't supported but someone else commented that it is supported in this thread, and in another thread, it says rclone doesn't implement proxies on their own and it should support socks5 because the go get library being used supports it, and the FAQ also indicates that socks5 as a proxy protocol is supported and I remember in one Github issue a member says the reason to explicitly specify protocol in the environment variable is that there are socks proxies other than http/https ones. I would suggest at least print something in the log if the specified proxy isn't supported.
Also, the issue you linked seems to be specific about FTP/SFTP remotes, while OneDrive should be using http//https, no? At least it's dumping a bunch of http headers when I use the --dump headers option.
Updates: Can confirm it's not a problem with the socks proxy. I created an http proxy instead, and still rclone isn't using it.