Restricted plugin header field(s) found: 'GitHub Plugin URI'.
This is the first time I'm seeing this message. This is a very common practice and it feels odd that this is flagged. I know people use it update from GitHub instead of the WP repo but it's always been allowed. You had to have another plugin to even do that. Devs use it all the time though. It feels like the drama is spilling over into other aspects. This is tightening the grip and forcing devs and users to use the WP directory exclusively. Feels like a little thing that was taken away. End of the world, no. Kinda like shrink-flation. I'm upset but I'm still going to do it. I'm still going to buy the smaller bag of chips.

I disagree. The plugin check is for plugins that are on WordPress.org.
It kind of makes sense to not allow a plugin on WordPress.org get updates from a third party repo. Seems like that would allow all sorts of shenanigans where a dev with bad intent could upload a plugin to WordPress.org that passes review and then have different code in a GitHub update that does something bad.