It feels like a cliche now. Read the article and of course, they're sunsetting something else.
That seems to be what they're doing?
This is not an "upgrade." This is "replace product with a different product in the same space." Old GA data is incompatible with GA4 data, and there is no way to bring data from one into the other. Google is discontinuing Google Analytics, and applying the Google Analytics brand to Firebase Analytics.
Nothing carries over. Configuration, implementation, goals, user permissions, historical data, nothing. It all has to be re-built from scratch.
The Google deprecation team has really outdone themselves this time. I really would have thought they'd deprecate Gmail before Google Analytics! I've got to imagine there are legal reasons behind this, because no product team could sincerely believe that this is a good idea for the product, right?
Yes. That's what the original post and the entire discussion here is about.
I imagine you'll hear a lot of that in the near future
It's like when, e.g., Heroku sends me an email saying I need to move apps off of a stack they're retiring. They're not killing off my app; I just need to run the command or agree to a maintenance window so it keeps working after a certain date. If I for whatever reason refuse to do anything, I can't seriously claim they're shutting me down. Especially with a long notice period.
"Doing so will allow you to build the necessary historical data and usage in the new experience, preparing you for continuity once Universal Analytics is no longer available."
That doesn't seem to indicate your old data comes with.
Anyway, I don't mean to take away from your moment to hate on Google. :) It's just not a classic Google discontinuation like when they eventually shut down Stadia or whatever.
Nobody wants to move to GA4. It has nothing UA doesn't, and UA has lots of features GA4 doesn't. If they're sunsetting UA next year, there's no way it'll have improved enough by then to be a fully functioning replacement. It has a cleaner structure than UA, because it's dropping a decade of cruft, but that doesn't really help when it just doesn't do as much.
The people that are moving to GA4 are running both UA and GA4 in parallel, so that they'll have a history set when UA shuts off. Those are companies that are paying attention. I would be surprised, by the 2023 date, if even 25% of the UA installations have switched to GA4. (Of course, all the larger companies will have.)
Side note... I looked into Shopify a month or two back. They have a drop in UA implementation that is almost as easy as clicking on a checkbox. Not only do they not have a wizard for implementing GA4, they say it's not even possible for you to add manually. No due date was given. A lot of sites have UA built in as the assumed forever default.