I don't know if anyone it will matter to is going to read this, but regardless:

Part of the reason this banner really cheeses me off is because it makes it obvious the Classic theme is going to be retired in favour of the Modern one inevitably.
I just really wish that, seriously, if you were going to do it, you should've just done it immediately, force people over to Modern, and explain why. Instead, by going with a half-measure of that permanent banner, you're just both annoying people further, and encouraging them to become further entrenched and even more annoyed and upset when the change does come.

Just... seriously. Just, explain to people why the change to Modern has to happen. Make it swift, not drawn out. Don't persist with the annoying banner that people are going to ad-block and risk plugins like Ublock Origin automatically blocking future IMPORTANT news from the website simply because it will assume that's also an ad banner - this is part of the reason I'm so annoyed! The site's users are being trained to treat anything in the header like an annoying ad now, instead of potentially important news.

Yes, I've noticed the journal ratings system doesn't work on the Classic theme. Including for reading them. That is probably why you have all rushed out that banner. But that was still the incorrect way to go about it.

I sincerely believe the stragglers would've been not so upset if you just explained in honesty why the change to the new theme was mandated - because it is necessary to ensure that the journal ratings system doesn't become an issue, to ensure that security updates can be properly maintained, and prevent things such as the recent Notes bug from happening because one of the two themes is being much less properly maintained.

I am begging you, be open, communicative, and honest speaking with the userbase. Treat them, and yourselves, like people.
Because you are people, and everyone knows you are people.
And people hate when people put on a business-like facade.
And people are generally forgiving when you admit something is a mistake, and apologise for it meaningfully - without being forced to.

This is a good website. But y'all make it really hard to say that sometimes with choices such as this one made. And this banner, it's really annoyed a bunch of the more infosec minded folks I know, because of the user behaviours you all are encouraging.